Corundum Americas

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Corundum Americas
Al₂O₃





Corundum is a common and attractive mineral that are or has been mined as a gemstone or as an industrial product at various localities around the world. The corundum article is therefore split into a multiple articles, one for each continent as follows:

Corundum main article
Corundum Africa
Corundum Americas
Corundum Asia
Corundum Australia
Corundum Europe and Russia


Although neither North or South America is not considered a prime supplier of neither corundum specimens or gems today, several good locations and excellent specimens can be found. The locations included in this text includes both historical locations, current and a few locations with the potential for an exciting future.

In the period from the 1850-ties to the 1940-ties corundum was mined both as gems, abrasives and for industrial use such as bearings on the East Coast of the USA , abrasives in Ontario Canada and gems in Montana USA. many of the best corundum specimens found in America dates back to this period, and several museums must have some outstanding specimens in their collections.

Today Yogo Gulch in Montana still produces natural blue sapphires, whereas fee-digging for gem rubies and sapphires is a well established tourist activity in both North Carolina and Montana. Some lucky diggers can have jewellery made from self-found jewels.

In addition to these classic locations still producing both gem material and well formed collectors specimens,Brazil, Columbia, Arctic Canada and Greenland have locations that are either poorly exploited or still in a prospecting phase. Some of these locations have already produced nice specimens, and, depending on future development, may produce even more.

The best corundum specimen for many of the locations entered in this text was found between 100 and 150 years ago, and for some of the newer locations, very few images are uploaded to Mindat. The photos in this text are therefore not always representative for the quality of specimens found at these locations. This should be taking into account when reading the article.

Corundum has in many cases been formed by regional geological processes, so that it occurs at many more locations than included in this text, and the ones included are not necessarily the best. This is particularily valid for the Eastern part of the USA and Ontario Canada.

I also have to say that some of the old literature are really outstanding in their description of the localities and the corundum found there, and I recommend anyone with an interest in corundum or American mining history to search the web and download some of these publications. Many of them are available for free as full text pdf documents.


Corundum
Brazil
Goiás

4,5cm crystal	© Martins da Pedra

Goias is one of the inland states of Brazil. It covers an area of 340,086 km², roughly 50% larger than Great Britain. The locality information might therefore be considered as rather approximate.

The best written reference I have found for a Goiás corundum locality is Marundito, a road cut on the "Petrolina Nerópolis Goiás, near the junction towards Damolândia where a predominiantly corundum/margarite rock is formed by Ca and Al enrichment and Si/Fe leaching caused by hydrothermal/metasomatic action on the regional gneiss.

No information are given on how the corundum occurs, and I have no idea if this is the locality that has produced the pictured corundum crystals.

Literature: Programa Levantamentos Geológicos Básicos do Brasil


Corundum
Brazil
Minas Gerais



Corundum has been known in Minas Gerais since early in the 20th century, but has been overshadowed by all the other gems and minerals found here. It was not until the Indaiá deposits were found in the 1990-ties the potential for sapphire and ruby mining was identified.

Most deposits of corundum is associated with Plio-Pleistocene paleoalluvial deposits. Deposits are currently in the deepest parts of the sedimentary valley fills. The source rock of the corundum has not been identified, but the sediments including the deposits of corundum are medium to high grade metamorphic rocks, such as schists, gneisses, granulites and charnockites.

There are currently small scale mining take place in four different locations. The potential is apparently in place for industrial mining, but the lack of tradition ofr ruby and sapphire exploration as well as environmental issues prevents this.

Literature: Antonio Liccardo; Ester Figueiredo Oliveira; Hanna Jordt-Evangelista(2005): Rubi e safiras de Minas Gerais, Brasil, Revista Escola de Minas vol.58 no.3 Ouro Preto July/Sept. 2005


Corundum
Brazil
Minas Gerais, Indaiá

Sapphires of colors ranging from deep blue to violet, almost purple are found in alluvial and colluvial deposits of Indaiá. The crystals have anhedral is usually small (<1cm) and some show a moderate color change from blue to purple-blue and purple to purple-violet.
In terms of color and transparency, sapphires show a good potential as gem material, and the potential can be increased with suitable heat treatment.

Corundum
Brazil
Minas Gerais,Malahide

The Malahide sapphire occurs in euhedral crystals transparent in the typical barrel shape and size are usually small (<1cm). The majority of crystals are zoned, with an intense blue coloration and colorless exterior. The crystals normally show good transparency, tending to translucent.


Corundum
Brazil
Minas Gerais,Palm

The crystals are euhedral predominantly red in color (pink sapphire or ruby), to a lesser extent also violet or purple, and rarely blue, with elongated prismatic habit and "barrel", with size ranging from 0.5 to 4cm. Some of the crystals are transparent crystals, but most range from opaque to translucent


Corundum
Brazil
Minas Gerais,Sapucaia

The sapphire crystals in Sapucaia occurs as euhedral, subhedral and irregular fragments, in blue, purple, violet and black colors. Crystals are normally found as elongated hexagonal prisms often ending in bipyramids. The outer surface of the crystals is normally smooth and often covered with microcrystalline muscovite. The crystals average around 1 cm long, but larger crystals up to 8 cm long.
The crystals are normally opaque to transluscent, but show color change (blue sapphires in natural light becomes violet under incandescent lighting), and some black sapphires show six-pointed asterism.


Corundum
Brazil
Paraíba



Corundum
Brazil
Tocantins, Peixe alkaline complex

The Peixe complex is a 150 km2 corundum-bearing, coarse grained syenite complex. The syenite intrusion covers a surface area of approx 30x5 km and it penetrates a Mesoproterozoic metasedimetary sequence. Lenses of syenitic pegmatites (outcrops to about 100m long) and granitic pegmatites (outcrops about 500m long) are located in the central and eastern part of the syenite body.

Corundum occurs in the silica undersaturated portions of the intrusion as disseminated phenocrysts up to one cm in nepheline syenite and as bluish, opaque crystals up to a couple of dm (20cm) in related syenitic pegmatites. This occurance of corundum are interesting for petrologists, as it has formed at low pressures (2,5-3kbar).

Literature:

Philippe Rossi , Geraldo F. Andrade , Jose C. Gaspar(1997): The Peixe (Tocantins, Brazil) Mesoproterozoic corundum-bearing syenite pegmatite complex age considerations on its origin and regional XXXIX CONGRESSO BRASILEIRO DE GEOLOGIA

Flávio H. Freitas-Silva, José Carlos Gaspar, Geraldo F. Andrade, Luiz F. W. Kitajima(1998): Low pressure corundum crystallization in the Peixe Alkaline Complex (Tocantins, Brazil) as evidenced by fluid inclusion characterization, abstract, Brazilian Geology Congress, 40th,Belo Horizonte,


Corundum
Canada
Nunavut Territory, Baffin Island, Kimmirut (Lake Harbour), Beluga sapphire property

In 2002 gem-quality corundum (sapphire) was found 1.5 km to the southwest of Kimmirut, Nunavut. Since then a substantial effort has been put forward to map the extent of the of the location, and also to test the market potential for the gems. In all 15 corundum locations has been found with scapolite, coboltoan blue spinel other calc-silicate minerals associated with the Paleoproterozoic Lake Harbour marble and high-grade metamorphic rocks.

The sapphire typically occurs as elongated barrel shaped crystals. The largest recorded crystal was 20 cm long, but the crystals are normally much smaller. The majority of crystals are colour-zoned, displaying concentric and irregular variations in colour from colourless through shades of dark to light blue. Light yellow sapphires have also been found.

Literature:

A.M. CADE, G.M. DIPPLE, AND L.A. GROAT (2005): Geochemical study of the Kimmirut sapphire occurrence, Baffin Island: Canada Goldschmidt Conference Abstracts 2005
Alpine gems- website
True North Gems - Website


Corundum
Canada
Ontario, Hastings Co., Carlow Township, Logan Corundum occurrence

,

Corundum, 4 cm crystal	© M. Adamowicz

The Logan cuts are three small workings near the larger Burgess mines. Together with a series of small claims, prospects and quarries in the vicinity, they delivered corundum ore to the mill at Burgess, where the ore was processed to emery.

The corundum at the Logan cuts are found as elongated crystals in a nepheline-corundum plagioclase rock. This alkaline rock is part of a 130km long discontinued belt with nepheline syenites and -gneisses between Brudenell and Glamorgan Townships in roughly halfway between Ottawa and Toronto, Ontario, Canada. These rocks often carry corundum as a rock forming mineral, sometimes exceeding 10% of the total bulk volume, and extensive prospecting in the first couple of decades of the 20centuries have exposed a large number of locations, and the Logan cuts is one of the locations that still produces good specimens.

The Logan cuts are located not far from the Burgess mine and should be accessible by a 4x4 wheel drive, but it may be necessary to hike for up to 1 ½ hour, based on where you have to park your car. The Logan Cuts consist of three corundum cuts there; The eastern cut which is 200 ft long x 25ft wide and 12-15 feet deep. The rocks exposed enclosing a band of light nepheline-corundum-plagioclase gneiss 5-10 feet wide. Muscovite and large bronze corundum crystals, up to 6 inches in size, occur in the nepheline rich bands and in altered zones between the nepheline rich rocks and the syenite, giving a total corundumbearing width of about 12 ft.

The central cut is 75 feet long in an east-west direction, 30 to 40 feet wide, and has a face 10-25 feet high. Here, there is a series of banded pink and buff syenites enclosing a 6-foot band of hybrid buff corundum-gieseckite syenite.
Barrel-shaped bronze and green crystals of corundum up to 5 inches long occur in a corundum syenite pegmatite zone, 6 feet wide, on the east face. This zone runs 10-15 percent corundum.

Thirty feet to the southwest there is a third cut on the west face of the hillside. The cut has a length of 70 feet in a north-south direction, a width of 30 feet, and a face up to 25 feet in height. The cut exposes interbanded pink,
buff, and grey plagioclase syenites. A pegmatite corundum syenite zone, 4 feet wide, exposed in the east wall runs 10-15 percent corundum. A second corundumzone occurs at the base of the cut.

This description is mainly derived from Hewitt (1954) who lists 30 corundum prospects in the Monteagle and Carlow Townships, not all of them carrying corundum in large well formed crystals. Martin(1983) provides a more extensive listing covering the entire Algonquin region. All the corundum deposits in this area are found in similar rocks, and geologists have discussed the origin of these rather special rocks ever since the first discovery of corundum in the area in 1847.

Literature:

Lours Moyn(1949): PETROLOGY OF THE NEPHELINE AND CORUNDUM ROCKS OF SOUTHEASTERN ONTARIO, American Mineralogist Vol 34. page 736pp.

D. F. HEWITT (1954): Geology of Monteagle and Carlow Townships, SIXTY-THIRD ANNUAL REPORT
OF THE ONTARIO DEPARTMENT OF MINES

Wendy Martin (1983): Industrial Minerals of the Algonquin Region, ONTARIO' GEOLOGICAL SURVEY
Open File Report 5425

GREGOR M. ANDERSON, CLAUDIO CERMIGNANI (1991):
MINERALOGICAL AND THERMODYNAMIC CONSTRAINTS ON THE METASOMATIC ORIGIN OF THE YORK RIVER NEPHELINE GNEISSES, BANCROFT, ONTARIO, Canadian Minerologist, Vol-29, pp. 965-980


Corundum
Canada
Ontario, Renfrew Co., Raglan Township, Craigmont Mine



The Craigmont corundum mine has been the largest corundum mine in Canada. It was in operation in two periods, first period from 1900 to 1921, and a second period from 1944 to 1946. The production of corundum in the period from 1919-1921 and the second operations period came exclusively from reworking the tailings of the mine. Obviously this has made it more difficult for mineral collectors to find good specimens in the tailings.

The produce at Craigmont was abrasive products, as the corundum from the Ontario corundum belt is not gemmy. During its heydays, the Craigmont mine supplied approximately half the world’s emery production. Although it is estimated that only 10% of the resources ( ref Storey and Vos(1981), Sattely(1941) consideres the mine as almost depleted) has been produced. Regardless of the remaining volumes, it is quite unlikely that the Ontario corundum will ever become an exploitable resource again as emery today is produced from bauxite.

Craigmore was at a time the source of the best corundum specimens in Ontario, and almost half of the nearly 70 corundum species in the Royal Ontario Museum of Mineralogy at Toronto is from Craigmont, including the largest single crystalfound; an 8 in (ca 23cm) long, 6 1/4 inches (ca 16cm) wide, and weighing 20 pounds.

Corundum occurs in several of the rock types found at Craigmount, and it’s occurance ranges from small, mm sized anhedral grains to large well formed crystals. The corundum occurs in bands of gneiss, syenitepegmatite,and nepheline rocks interbanded with the gneisses. The corundum crystals are usually bronzy-brown in colour on a fresh fracture. Most of the crystals are rough-surfaced and barrel-shaped except those found in the nepheline bands, which are smooth-surfaced, sharp-angled, and more tapered.

The literature references provides a vast amount of additional information on the Craigmont operations, production, geology and mineralogy, as well as similar information from other corundum deposits in Ontario.

Literature:

J. SATTERLY (1944): Mineral Occurrences in the Renfrew Area, FIFTY-THIRD ANNUAL REPORT OF THE
ONTARIO DEPARTMENT OF MINES, VOL. LIII, PART III, 1944

CC Storey, M.A Vos (1981): Industrial Minerals of the Pembroke-Renfrew Area, Part 2, Ontario Geological Survey Mineral Deposits Circular 22

J. Satterly(1977): A CATALOGUE OF THE ONTARIO LOCALITIES REPRESENTED BY THE MINERAL COLLECTION
OF THE ROYAL ONTARIO MUSEUM, Ontario Geological Survey Miscellaneous Paper MP70


Corundum
Colombia
Cauca and Nariño departments



Corundum has been known from Columbia for a long time. The earliest written account still available is from Raleigh (1596): “…Captaine Whiddon, and our Chirurgion Nich. Millechap brought me a kinde ofstones like Saphires, ….and they promised to bring me to a montaine, that had of them very large peeces growing Diamond wise: whether it be Christall of the mountaine, Bristoll Diamond, or Saphire I doe not yet knowe, but I ope the best.....”.

The corundum (ruby and sapphires) deposits are situated in recent volcanic rocks in the Colombian Andes. Corundum are found in a some 60 km2 large area in the high Patia valley at the border between the Departments of Cauca and Nariño.

In this area, up to 200m thick garnet bearing andesic tuffs rich in volcanic bombs lies on top of cretaceous diabasic rocks. The composition of these bombs are both volcanic ( andesite and basalt) and xenoliths of a wide range of metamorphic rocks of various composition and grade.

It is unclear whether the corundum originates from the volcanic rocks, the xenoliths or both, as crystals and pebbles are recovered from numerous stream beds, terraces, gravel, and shallow creeks on both sides of the Río Mayo, and from sands of the Río Platoyaco.

Corundum is found as more or less transparent crystals or rounded pebbles rarely exceeding 1cm in size. The crystals show a variety of colors (near colourless, greenish-blue, greyish-blue, brownish yellow, yellowish-green, brownish-red, and multicoloured) and may occasionally form sharp hexagonal prisms.

It is difficult to say how rich this location is, as it lies in a remote are with a history of political instability that makes systematic research, production and trade difficult.

Literature: Jean-Marie DUROC-DANNER(2002): A study of Colombian corundum, DIPLÔME D’UNIVERSITÉ DE GEMMOLOGIE, Devant l’Université de Nantes U.F.R. des Sciences et des Techniques.


Corundum
Greenland
Kitaa (West Greenland) Province, Nuuk (Godthåb), Fiskenaes (Fiskenaesset; Qeqertarsuatsiaat, Aappaluttoq),


True North Gems are in the final planning stages of the first large scale industrial mining operations for rubies in the type locality of sapphirine and kornerupin. Large scale prospecting has revealed 18 ruby locations in a 3600 km2 mining district. The references give a detailed description of each of these locations.

Ruby is found in a 2,86Ga layered intrusion called the Fiskenaesset anorthosite complex. and is tectonically interleaved and infolded with Mid-Archean gneissic basement. The entire terrane has been subjected to at least one episode of Late Archean, granulite facies metamorphism with amphibolite facies retrograde involving 3 stages of regional folding.

Ruby has been formed by metasomatic (16 locations), metamorphic(1) and hydrothermal (1) processes near the contact between Cr bearing anorthosite and surrounding amphibolite. It occurs as both anhedral (with pargasite and sapphirine) and tabular to prismatic euhedral crystals with pargasite. Crystals rarely exceeds 2 cm in the largest dimension, but crystals and crystal groups with up to minimum 15 cm long prismatic crystals are known, sometimes as very nice specimens.

Literature:

Kamolwan Thirangoon (undated, 2007 or later), Ruby and Pink Sapphire from Aappaluttoq, Greenland Status of on‐going research, Status report GIA Laboratory, Bangkok
K. Secher and O. Johnsen(2008): Minerals in Greenland, Geology and ore 12/2008

WILLIAM R. ROHTERT(2005): 2005 Report on Field Activities for the Fiskenaesset Ruby Project,Greenland, True North Gems report 43-101


Corundum
USA
California, Riverside Co., San Jacinto Mts, Unnamed Corundum occurrences

Corundum 105mm crystal	©

This text is quoted from the Mindat locality page: See Mindat locality page

"Geology:
The deposits are located along the contact of granodiorite/quartz diorite host rock and metamorphosed marine sediments. Several small biotite schist bodies at the contact zone contain random sprays and clusters of corundum crystals, up to 2 feet long and 3 inches in diameter. The crystals are included with biotite so severely that in some crystals there is partial replacement. Much of the schist has been decomposed to an iron-stained micaceous clay, which contains inclusions of quartz and feldspar. Quartz veins with feldspar and garnet occur nearby.

History:
According Fred Rynerson, the first report of corundum crystals from the area was made around 1924, by an unnamed woman about 60 years old that had brought a dozen crystals to Ward's Lapidary shop in San Diego for appraisal. The largest crystal was said to have measured approximately 2 inches long, and 3/4 inch at the base, tapering to 1/2 inch at the top. The woman reported that the crystals were scattered over the side of a small hill behind her house. Four years later, Rynerson searched several collections in Riverside County for the source of these crystals, but was unable to find any information about the deposit.

In 1939, large crystals of corundum embedded in mica schist were submitted to the Department of Geology at UCLA, by Mr. B. G. Funk of Los Angeles. These specimens showed sapphire-blue cores, with a progressively zoned gray colored outer rim included with micaceous material. The area was visited around 1940 by Joseph Murdoch and Robert W. Webb, who reported corundum crystals having been found as float in many parts of the San Jacinto Mountains. Several decades later, Mark Rogers reported that several crystals up to 12 inches long, both loose and in schist matrix, had been collected from the area in the late 1940's by a married couple of Asian decent.

In 1980, brothers Ken and Dana Gochenour visited the area several times and eventually discovered a small outcrop of corundum-bearing schist that contained crystals up to 4 inches in length. In 1999, the Gochenours reported finding the remains of an old working that contained a dark biotite schist with broken crystals up to 12 inches long and an inch in diameter. This schist had some crystals that were up to 7 inches long in situ. Several other locations were later discovered while prospecting along the surface, and over 150 pounds of large corundum crystal segments were said to have been collected from the area."

Literature:

K. L. Gochenour (2000): Corundum Crystals from the San Jacinto Mountains, published as a Mindat Articlke by Scott L. Ritchie


Corundum
USA
California, San Bernardino Co., San Gabriel Mts, San Antonio Canyon, Cascade Canyon

Corundum crystal 1 in. long	© The-Vug.com

Corundum is found in a metamorphic rock consisting of 90-95% sodium and potassium feldspar, 5-10% corundum, and minor muscovite mica, monazite, sillimanite, pyrite, and rutile. The corundum bearing rock is part of a metasedimentary sequence consisting of limestones, quartzites and gneisses intruded by Cretaceous granitic intrusions. The peak metamorphic conditions (ca 800 deg C) was caused by these granites, causing corundum to be formed

The corundum is normally pink/red/violet and are generally termed ruby, and are found as prismatic hexagonal crystals up to 1 inch long. The corundum may contain up to 3%vol rutile, which has been used to estimate the temperature of formation.

Corundum is still possible to find at this location, and a number of field trip reports are published on the web.

Literature

SHEPHERD, Hannah V., JOHNSON, Elizabeth A., and LOGAN, M. Amelia V. (2010) ZR-IN-RUTILE THERMOMETRY OF A RUBY-BEARING METAMORPHIC ROCK, CASCADE CANYON, SAN BERNARDINO COUNTY, CA ( Abstract), Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting Paper No. 65-24

Mindat location page, seeMindat location Page


Corundum
USA
Idaho, Adams Co., Meadows District, Rock Flat Placer



The Rock(y) flat placer is one of many alluvial corundum deposits in Idaho that was discovered in conjunction with gold prospecting. The rumour says that the Rock Flat Placer also was prospected for diamonds, but without any success as no diamond finds are confirmed from here. The corundum is normally dull, grayish opaque material, although light blue and bluish green transparent stones can be found. Facetable material is scarce. Some of the translucent material may cut into attractive cabochons showing chatoyancy or even asterism.

Crystals are normally rough, imperfect and worn, and the pictured specimens seems to be typical, although not the best, for the locality.

Literature

John A. Beckwith (2007 9th edition): Gem minerals of Idaho, Caxton Press.

Corundum
USA
Idaho, Valley Co., Smiths Ferry Area, Bowman Corundum Occurrence,

This is the only location ( or at least one of very few) in Idaho where corundum can be found in solid rock. It occurs as megacrysts in up to 30ft diameter schist inclusions in a granodiorite of the Idaho batolith. The schist constitutes of 15-20% corundum occuring in short prismatic or tabular, often irregular, light gray to buff crystals up to 3cm long and 2 cm wide.

Literature:

Verne C. Fryklund Jr. (1951): Note on the occurencve of corundum in Idaho: American Mineralogist V36, No 9-10 pp 776-777.

Corundum
USA
Montana, Gallatin Co.,Gallatin Gateway

Corundum 48mm crystal	© Joseph A. Freilich, LLC

Corundum occurs in thin, lenticular layers of biotite-sillimanite gneiss in a series of highly metamorphosed pre-Cambrian rocks southwest of Bozeman Montain, in Gallatin and Madison Counties. There are also other corundum localities in teh Precambrian rocks Three deposits has been explored and partly developed as potential sources of abrasive corundum.The Gallatin Corundum deposit has been the most prominent of these. The mine produced 350 tons of corundum concentrates from a 2,100 pound per day rated mill at the mine. However, the mine failed to show a profit and was closed. The mine was idle until 1943 when the U. S. Bureau of Mines did some exploratory work. The mine was explored for a length of nearly a mile and a width of 400 feet in several audits and shaft. Nice corundum specimens can still be found

Corundum bearing rocks are found as lenses in gneiss, and are believed to originate from metamorphosed alumina-rich sedimentary beds in a series of shales and sandstones. The corundum occurs with feldspar, mica, and sillimanite. The lenses or layers range from a few inches to 6 feet in width and from a few feet to more than 800 feet in length. All the bodies of corundum-bearing rock are parallel to the foliation and major compositional layering of the gneiss.

The corundum crystals vary in size from microscopic grains to prismatic crystals several inches in length, and crystals a foot long has been reported. Many of the crystals are surrounded by aureoles of feldspar. Most of the larger corundum crystals are euhedral, with a characteristic tapered prismatic or barrel shape, although platy, distorted, and intergrown crystals are not uncommon. The corundum is opaque to slightly translucent, and most of it is light blue, dark blue, or gray. Lilac corundum occurs at one locality. No corundum of gem quality has been found in these deposits.

Literature:

S. E. CLABAUGH andYt C. ARMSTRONG (1950): Corundum Deposits of Gallatin and Madison Counties, Montana, GEOLOGICAL SURVEY BULLETIN 969-B, CONTRIBUTIONS TO ECONOMIC GEOLOGY 1949-50

STEPHEN E. CLABAUGH(1952): Corundum Deposits of Montana, GEOLOGICAL SURVEY BULLETIN 983, USGS

Montana Department of environmental quality


Corundum
USA
Montana, Gallatin Co.,Gallatin Gateway, Bozeman Corundum Co. Mine

Corundum 2,2 cm crystal	© M.Adamowicz

The Bozeman Corundum ione is one of the corundum mines in Gallatin County. The deposit was located in 1902 and first worked by the Bozeman Corundum Company. About 1,000 tons of rock was sent to the mill at the Gallatin mine (see above). The Bozeman mine closed after the closure of the Gallatin mine left it without a mill. The mine was developed in two groups. The northern deposits were explored by 14 trenches, a shaft and two short adits. The southern deposits, 600 feet southwest, contained 16 trenches, four pits and one adit. In 1944, the U. S. Bureau of Mines reopened three adits and bulldozed about 4,000 feet of trenches (Heinrich 1948).

Literature:

Montana Department of environmental quality

Corundum
USA
Montana, Granite Co., Rock Creek District, Gem Mountain Sapphire Mine (American Sapphire Gem Mine; Chaussee Sapphire Mine)

The Rock Creek sapphires are generally similar to the sapphires from the Missouri River but differ in the typical shape of the crystals. The sapphires are mainly very pale green with rare pink sapphires. Most are small, many less than about 6 mm. Color is enhanced by heat treatment. Sapphires are mainly irregular equidimensional forms. There are some hexagonal tablets, but they are rare. Inclusions are relatively rare. There appears to be more of the larger sized (greater than a half inch) material at Rock Creek.

Similar type material can be found at the South Fork of Dry Cottonwood Creek.

Literature:

STEPHEN E. CLABAUGH(1952): Corundum Deposits of Montana, GEOLOGICAL SURVEY BULLETIN 983, USGS
Richard B. Berg (2011), Personal communication

Corundum
USA
Montana, Judith Basin Co., Little Belt Mts, Yogo District, Yogo Gulch

Corundum ca 0,8cm	©

Yogo Gulch is the prime US location for gem corundum, and commercial mining for sapphires has taken place in irregular intervals since 1896. The sapphires found at Yogo are special in that the majority of gemstones found are of a distinct blue color, and similar to the Kashmiri sapphires, they do not require any treatment to obtain an attractive blue color.

Yogo sapphires are known for their uniform, well-saturated blue color; relative absence of inclusions and zonation; and high luster and brilliance in both artificial and natural light; they do not require heat treatment, and as much as 25% of the corundum has been gem quality. The only drawback is that the Yogo sapphires are very small, with crystals rarely exceeding 5 carats rough weight. The sapphires often show a tabular habit, making cutting difficult. Only a handful crystals or crystal groups exceeding 15mm are known. Yogo sapphires have very few impurities, containing only iron (0,41-0,67 wt% Fe2O3), Ti (o,o2-0,05 wt% TiO2 and Cr (0,03-0,08 wt% Cr2O3) above the electron microprobe detection limit at ca 0,01wt% oxide.

Sapphires was first found in river gravel during gold mining, but was soon found in lamprophyre dikes (50Ma) cutting a limestone interbedded with clay horizons. Corundum occurs in the lamprophyre as an accessory mineral, containing no more than 20-60 carats pr. ton rock on average. The lamprophyre contains xenoliths from several different rock types, including a cyanite/quartz rock. Xenoliths from the Precambrian basement rock indicates a deep origin of the dikes. Whether the sapphires has been formed in the original magma(phenocrysts) or through interaction with surrounding rocks(Xenocrysts) has been debated ever since their discovery, but it appears that a xenocrystic origin is the more likely.

Literature:
Joseph Hyde Pratt (1901): The occurrence and distribution of corundum in the United states, Published by United States Geological Survey

STEPHEN E. CLABAUGH(1952): Corundum Deposits of Montana, GEOLOGICAL SURVEY BULLETIN 983, USGS

Guylaine Gauthier(1995): Mineralogy, Geochemistry, and geochronology of the Yogo dike sapphire deposit, Montana, Thesis for the degree of applied Science in the faculty of graduate studies ( Department of gelogy), The University of British Colombia)

Keith A. Mychaluk (1995): The Yogo Sapphire Deposit(abstract), Gems & Gemology Volume 31, Number 1

Richard B. Berg (2009), Montana Sapphires – Past, Present, and Future, Modified from Preprint 09-029 SME Annual Meeting



Corundum
USA
Montana, Lewis and Clark Co., Helena District (Spring Hill District), Helena, Helena area, Missouri River gravel bar



Sapphires were first found in Montana in the gravel deposits along the Missouri River northeast of Helena. The deposits in which sapphires occur are chiefly gravel beds lying on benches or terraces that rise to elevations as great as 200 feet above the river level. These gravel deposits are called bars, and gem corundum can be found in several of these bars along the river for approximately 20 miles in the northeastern direction from Helena.

The corundum from the Missouri rarely exceed 10 mm in length, but are generally larger than the Yogo Gulch sapphires. Sapphire can frequently be found as slightly rounded tabular crystals with hexagonal outline. Their color are usually pale, and of a lightgreen to light-blue color, but nice yellow, green, blue and red stones have been cut. Heat treating the corundum from here will enhance the color and give blue stones.

Missouri river sapphire has been of less value than the blue Yogo Gulch sapphires, but have still been mined at infrequent intervals. Today several companies have a "dig your own sapphire" offering.

Literature:

STEPHEN E. CLABAUGH(1952): Corundum Deposits of Montana, GEOLOGICAL SURVEY BULLETIN 983, USGS

M.I. Garland, G.S. Henderson, and F.J. Wicks (2001): TRACE ELEMENT AND INCLUSION CHEMISTRY OF GEM CORUNDUM: EXTRAPOLATING THE SOURCE FOR THE MONTANA ALLUVIAL SAPPHIRES, Eleventh Annual V. M. Goldschmidt Conference

Corundum
USA
New Jersey, Sussex Co., Franklin Mining District, Franklin, Franklin Quarry (Moses Bigelow Quarry; Farber Quarry)

Corundum 10 cm specimen	© 2007 Peter Cristofono

Corundum occurs throughout the local extent of the Franklin Marble and close to but not within the orebodies. It can be found in many if the mines and quarries in the area, and was locally abundant. It occurs as somewhat deformed euhedral to subhedral crystals up to 13 cm in length. The most common color is blue or bluish gray, but violet and red crystals are also known. Nice specimens can be found in the collections of Harvard and Franklin museums.

Literature

Pete J. Dunn (1995): Franklin and Sterling Hill, New Jersey: the world’s most magnificent mineral deposits, published on [franklin-sterlinghill.com] in 2001


Corundum
USA
New Jersey, Sussex Co., Sparta Township, Limecrest Quarry

Corundum 4 cm crystal	©

The Limecrest Quarry has been operated in the Franklin marble since 1906. It was opened by Thomas Edison as a source for high Ca Lime. The quarry was filled with groundwater in 2003 and only the upper benches has been worked since then. Most of the rocks exposed in the quarry consist of Franklin marble, but this is intersected by thin gneiss horizons. The minerals formed in the contact zone between the marble and the various gneisses has made this quarry popular amongst mineral collectors. Corundum is one of them.

Corundum can be found at several locations in New Jersey and New York in the contact zone between aluminous gneisses and marble together with other skarn minerals such as spinel, scapolite and others.

Literature:

- Volkert, Richard A. (2010): Deep Drilling at Limecrest Quarry, Sparta, New Jersey, Unearthing New Jersey, Vol 6, No1


Corundum
USA
New York, Orange Co., Town of Warwick, Warwick

Corundum 4cm specimen	©

Corundum from Warwick can be found as well defined bluish or pink crystals with spinel and other calc-silicate minerals. Corundum occurs in the Franklin marble, which is a highly metamorphosed Grenville limestone (900-1000Ma) that extends through New York, New Jersey and Pennsylvania.

Literature:

James Dwight Dana (1837): SYSTEM OF MINERALOGY


Corundum
USA
North Carolina, Lincoln Co., Propst Farm



Corundum was first found at the Propst farm around 1970, when a hexagonal crystal was found in the soil. Rockhounds has been allowed to to dig on the property for a small fee, and several good specimens has been found. The corundum is found in course gravel in thin ( approx.. 1 ft) horizons in the soil. It does not appear that any corundum has been found in hard rock.
The corundum is normally found in hexagonal, tabular or short prismatic individual crystals, sometimes larger than 5 cm in diameter. Occationally crystal clusters or individual long tapered crystals up to minimum 10cm can be found. The crystals are normally opaque and pink, sometimes with red and/or blue zones or patches in the crystal.

Literature:

Will Heierman(2007): Propst Farm sapphires, www.corunduminium.com
Mike Streeter(2006): Propst Farm corundum, www.mcrocks.com


Corundum
USA
North Carolina, Macon Co., Cowee Valley, Ellijay District, Franklin, Corundum Hill Mine,

Corundum 10 mm specimens	© 2003 Rex Biggers

A series of small ultramafic bodies can be found in the Appalachian mountains on the North American east coast from Newfoundland to Alabama. These ultramafic bodies are of various composition and age, but of oceanic origin. Many of them are interpreted as remains of an island arc formed in the early phases of the closure of the Iaeptus ocean during the Tactonic orogeny. During this and the following mountain forming these rocks have undergone several methamorphic events, transforming the original rocks to serpentinites, talc-schists and related rocks.

Corundum Hill is one of these ultramafic bodies, and it is probably the one that has produced the widest variety of corundum, and I have therefore chosen to give a fuller description of the geology and occurance than I have done for the other similar occurances between New York to South Carolina. Corundum occurs in many locations in this area, and I have only included a handful in this article.

Corundum Hill is a dunite body exposed over an area of about ten acres, forming an intrusive body in mica schist and as such representative for geological environment hosting most of the corundum in the eastern USA. The corundum has, in this environment formed through metasomatic activity on the border zone between the serpentinite/talc rocks and the surrounding metapelitic (gneisses and carbonate rocks) or through the interaction with later intrusive pegmatitic veins.

Gordon describes the rock sequence at Corundum Hill like this:

"The corundum veins consisted largely of chlorite and corundum, or locally of corundum-bearing plagioclase. fn passing from an interior vein to the dunite, the following zones were encountered: 1. green chlorites; 2. grayish enstatite or anthophyllite, more probably the latter; 3. fi.brous talc; 4. weathereddunite; and 5. normal dunite. Similar zones were found in theborder veins.This has fomed both massive, granular rock-forming and nicely crystallized corundum, sometimes as large boulders and even large crystals."

The Corundum Hill was originally opened to mine for gems in 1870, but production of massive corundum soon took over as the main product, but it soon became apparent that profitable production was not possible. In the few years of operation, this location provided a number of great specimens, making it a very interesting location.

Although most of the corundum was massive and found in large cleavable masses in chlorite, well-formed hexagonal pyramids with basal and rhombohedral planes was formed. Sometimes these crystals could be really large, a 5ft 2in crystal weighing 312 pounds are mentioned, and multi-cm well-formed crystals was common. The corundum could also be transparent in smaller areas and both colorless, yellow, pink, red and blue gems are known. Many of them quite small but Pratt described a unique partly transparent 4 x 2 x 1 ¼” green crystal, “and several very fine gems could be cut from it.”

The corundum photos uploaded to Mindat does not reflect the quality of the specimens found in the late 19th and early 20th century, and many exquisite crystals from the Corundum Hill must be stored in museums throughout the USA.

Literature

Samuel Gordon, (1922) :CORUNDUM HILL (FRANKLIN), MACON COUNTY NORTH CAROLINA JOURNAL MINERALOGICAL SOCIETY OF AMERICA

E.B. Alexander: Serpentine Geoecology of the Appalachian and Ouachitan Orogen, undated paper on Soils and Geoecology

Kula C. Misra and Harry Y McSween(1984) Mafic and ultramafic rocks of the appalachan orogeny- an introduction. American Journal of Science Vol 284, April/May p 290-293

Joseph Hyde Pratt (1933): GEMS AND GEM MINERALS OF NORTH CAROLINA, JOURNAL MINERALOGICAL SOCIETY OF AMERICA

M. Riesco, K. Stüwe and J. Reche(2004), Formation of corundum in metapelites around ultramafic bodies. An example from the Saualpe region, Eastern Alps , Earth and Environmental Science Mineralogy and Petrology Volume 83, Numbers 1-2,

A Genth & W.C Kerr (1885): MINERAL LOCALITIES NORTH CAROLINA, being chapter 1 of the second volume of the geology of North Carolina

Joseph Hyde Pratt (1901): The occurrence and distribution of corundum in the United states, Published by United States Geological Survey


Corundum
USA
North Carolina, Macon Co., Cowee Valley, Jacobs Ruby Mine

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Corundum 3-9 mm specimens	© 2003 Rex Biggers

Corundum is found at several locations in the Cowee Valley, and a number of mines are open for the public to wash gravel for rubies. Although some of the mines are “enhanced”, meaning that the soil is enriched with corundum from other locations, nicely colored rubies have been mined in this area since 1893. In the early years these locations were compared to the Mogok, rubies, and even the jeweler company Tiffany’s Co was involved in the mining operations, but commercial mining ended in 1914.

The rubies are normally found as small hexagonal flat or tabular crystals rarely exceeding 15 mm in diameter, but prismatic crystals are known. Pratt gives a detailed account on the crystallography of the rubies, and describes the largest crystal found:

The finest piece of ruby was a rough hexagonal crystal that measured about one inch by one and one-half inch. It was estimated that from the transparent portion of this crystal a gem worth from $1500.00 to $2500,00 couldbe cut.

Although red is the most prominent color, various shades of purple, pink and other colors may also be found.

The rubies are found in horizons in the sediments and are washed from river beds or from soil, described by Kunz:

“Underneath the ruby-bearing gravel, comes a soft decayed rock to which the name of saprolite has been given,—a result of the decomposition of basic igneous rocks, in place. This is sometimes many feet in thickness, but gradually passes downward into the unaltered condition of the same rocks. Trial shafts show that this change begins from a depth of some 35 feet, when portions of the unaltered rock begin to be met with. The original rock, when reached, proves to consist of several related varieties, comprising amphibolite, hornblende-eclogite (garnet-amphibolite of some authors), and a basic hornblende-gneiss, with some feldspars (labradorite and perhaps anorthite).”

Literature:

George Frederick Kunz (1907): History of the gems found in North Carolina, North Carolina Geologic and Economic Survey, Bulletin no 12

A Genth & W.C Kerr (1885): MINERAL LOCALITIES NORTH CAROLINA, being chapter 1 of the second volume of the geology of North Carolina

Joseph Hyde Pratt (1901): The occurrence and distribution of corundum in the United states, Published by United States Geological Survey

Joseph Hyde Pratt (1933): GEMS AND GEM MINERALS OF NORTH CAROLINA, JOURNAL MINERALOGICAL SOCIETY OF AMERICA

Frank Festa (2011): Ruby and Sapphire Hunting in Franklin, North Carolina, Mindat Article

Various websites presenting the current mining operations and experiences


Corundum
USA
Pennsylvania, Chester Co., Newlin Township, Unionville, Corundum Hill

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Corundum was reported from near Unionville as early as 1836, and mostly massive corundum in a serpentine body, was sporadically mined for most of the 19th century. The total production is estimated to a few hundred tons. Even if well formed nearly transparent crystals are reported, they were not common.

Literature:

Nancy C. Pearre (1958): Corundum mining in the Piedmont province of Pennsylvania, Information Circular 13, Commonwealth of Pennsylvania, Department of Environmental Resources.


Corundum
USA
Pennsylvania, Lehigh Co., Upper Milford Township, Shimersville,

Corundum, specimen 5x3,5 cm	© Joseph Polityka

Corundum was accidently found here in 1882, and a small quantity was mined for emery, apparantly without any commercial success. The geology of the location is poorly mapped, but corundum is described to have occured in a "pegmatite cutting through a gneiss". I have included a quote from Miller, quoting the original report from the find:

Early in January last, a piece of what was once a large hexagonal prism of corundum terminated by pyramids, was handed us. The specimen we received was an end piece exhibiting a perfect hexagonal form, with pyramidal ending, and on the broken surface of the crystal, the color observed was blue. The weight of this specimen is five pounds. The original complete
crystal measured eight inches in length, and the diameter over the secondary axes is about four and one-half inches. On the exterior surface are observable here and there, magnetite crystals and these were the cause of the destruction of the original crystal soon after it had been plowed up. The farmer thinking he had made a valuable discovery and curious to know the appearance of the inside, broke the crystal into several pieces,one of these coming into our possession, after it had been carried about to various parties, for inspection and determination. Only very slight indications of any alteration are apparent on the exterior of the crystal. Soon after getting the above, we received another crystal, a double pyramid about five and one-half inches long and weighing over five pounds. Since the reception of the preceding, we obtained several cigar boxes full of smaller, well-defined crystals. All of our specimens were found near Shimersville, Lehigh County, Pa., and were thrown out while plowing. The district over which these crystals were scattered, and have been noticed, is rather extensive and is .already under lease, and “prospecting” for larger quantities has been commenced. Quite a number of medium sized crystals were sent to the Weissport Emery Works, there tested and declared excellent for technical purposes. We reserve our analyses of the above for a future communication.
(Smith and Thomas, 1882.)

Literature:

Benjamin L. Miller (?): Mineralogy of Lehigh County, Unknown

John Eyerman (1889): The Mineralogy of Pennsylvania


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Edited 15 time(s). Last edit at 09/12/2012 09:02AM by Olav Revheim.