Log InRegister
Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for EducatorsMindat ArticlesThe ElementsBooks & Magazines
Minerals by PropertiesMinerals by ChemistryAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
Search For:
Mineral Name:
Locality Name:
Keyword(s):
 
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
Mining CompaniesStatisticsUsersMineral MuseumsMineral Shows & EventsThe Mindat DirectoryDevice Settings
Photo SearchPhoto GalleriesNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day GalleryMineral Photography

Dissolved Bikitaite: Explanation for Hollow, Bladed Inclusions and Epimorphs, Strickland Pegmatite, Portland, Connecticut, USA

Last Updated: 18th Mar 2020

By Harold Moritz

INTRODUCTION

Mysterious acicular inclusions are abundant in miarolitic quartz crystals from the Strickland pegmatite, Portland, Connecticut, USA. Among the many minerals found in the miarolitic cavities are large quartz crystals that host frosty white to tan, rectangular, bladed to acicular, randomly oriented to flabellate inclusions. The inclusions range in length from millimeters to a few centimeters and are commonly abundant under one side, or near the surface of, distorted quartz crystals. No comparable mineral has been found at Strickland other than in these quartz crystals, and there is no obvious, common pegmatite mineral that fits their description. This is a mystery I have been trying to solve for decades, and in this article I propose a possible solution.

00450800015853162089365.jpg
Typical rectangular, striated, bladed inclusions (mostly voids with partially filling), found in many large quartz crystals from Strickland pegmatite miarolitic cavities. FOV is 10 cm.


The Strickland pegmatite was quarried and mined primarily for microcline, muscovite, and beryl from at least 1904 until 1952. Details regarding these operations and its geology and mineralogy can be found on its mindat.org page. Most germane to this article are the pegmatite's highly evolved chemistry and resulting complex mineralogy, particularly its relatively rare Li enrichment. Of the hundreds of pegmatite quarries in the state, only 10 exhibit significant Li concentration (Strickland, Fillow, Casey, Hewitt, Gillette, White Rocks/Riverside, Anderson #1, Hollister, Walden, Brack), and even fewer have abundant miarolitic cavities (Strickland, Fillow, Hewitt, Gillette, Brack), where quartz and other minerals have crystallized in open spaces.

If present, miarolitic cavities host the final stages of pegmatite crystallization, at which time nearly all of the magma has solidified into the essential rock-forming minerals albite, quartz, and microcline along with common accessory minerals, such as muscovite, almandine/spessartine, tourmaline, and/or beryl, and has become filled with a fluid — more akin to a hydrothermal solution than a magma. These pockets can shatter or collapse, due to pressure changes and gas buildup, but crystallization typically continues until all fluids are lost or used up. Shattered fragments of pocket crystals can continue to grow, resulting in overgrowths, weird crystal shapes, and inclusion-filled crystals. New minerals may form around the fragments, cementing them together into a sort of pocket breccia. As the temperature lowers from a magmatic 450°C to less than 200°C to 150°C, low temperature minerals more typical of a fault-hosted hydrothermal environment may appear (e.g., pyrite, calcite, fluorite, and more quartz), followed by zeolite and clay minerals at even lower temperatures. Radical changes in solution chemistry can alter or dissolve primary minerals formed earlier under a different set of conditions and precipitate their chemistry at lower temperatures as a suite of hydrous, secondary minerals. Most commonly affected by dissolution and alteration are the primary Be and Li minerals minerals beryl, spodumene, and lithiophilite. All of these phenomena occurred in the Strickland pegmatite.

MYSTERIOUS INCLUSIONS IN MIAROLITIC CAVITY QUARTZ CRYSTALS

Here miarolitic cavities up to about 1 m formed within the cleavelandite-quartz intermediate zone that was up to about 15 m thick. After pocket collapse, the shattered primary pegmatite minerals (quartz, cleavelandite, muscovite, elbaite) continued to grow — in particular large, distorted quartz crystals formed crystallographically aligned overgrowths around fragments of earlier crystals. To varying degrees, and more or less at the same time, these fragments were cemented by fine-grained, secondary minerals such as a K-rich albite, quartz, micas, cookeite, fluorapatite, hydroxylapatite, bertrandite (the most common secondary Be mineral here), and capillary tourmaline.

08545410015854583651071.jpg
Pocket collapse cleavelandite breccia cemented by secondary tan albite.
08335530015853162089881.jpg
Secondary mineralization after pocket collapse: tan albite, drusy quartz, mica, fluorite, pyrite.
08545410015854583651071.jpg
Pocket collapse cleavelandite breccia cemented by secondary tan albite.
08335530015853162089881.jpg
Secondary mineralization after pocket collapse: tan albite, drusy quartz, mica, fluorite, pyrite.
08545410015854583651071.jpg
Pocket collapse cleavelandite breccia cemented by secondary tan albite.
08335530015853162089881.jpg
Secondary mineralization after pocket collapse: tan albite, drusy quartz, mica, fluorite, pyrite.


Many large pocket quartz crystals to over 50 cm long have been saved from the Strickland pegmatite. They typically occur on a matrix of massive quartz and cleavelandite and are light smoky gray, commonly with frosty zones near their exterior that are probably caused by fluid inclusions. They can be peppered with fine-grained crystals of the ubiquitous secondary albite along with late hydrothermal minerals, such as more quartz, bertrandite, pyrite, fluorite, etc., which impart rough surfaces. The shape of the large quartz crystals is very commonly distorted; instead of the usual six-sided prism with pointed termination, they are stubby, flattened, rhombic, or otherwise complex, reflecting their origin as overgrowths from random quartz fragments that resulted from pocket collapse. But most interesting are the frosty white to tan, rectangular, bladed to acicular, randomly oriented to flabellate inclusions that many, if not all, of the large quartz crystals possess. The inclusions range in length from millimeters to a few centimeters and are commonly abundant under one side, or near the surface of, distorted quartz crystals, suggesting that the included crystals grew on, or proximal to, the engulfing distorted host. But they can completely fill up the interior of smaller, undistorted quartz crystals, which evidently grew in the collapsed pockets from scratch.

00858570015831916999624.jpg
Large smoky quartz crystals on cleavelandite/quartz zone matrix.
03437230015831916995340.jpg
Complex quartz overgrowth.
08237000014950770277354.jpg
Large smoky quartz crystals on cleavelandite/quartz zone matrix.
03437230015831916995340.jpg
Complex quartz overgrowth.
08237000014950770277354.jpg
Large smoky quartz crystals on cleavelandite/quartz zone matrix.
03437230015831916995340.jpg
Complex quartz overgrowth.
05267410015831917003441.jpg
Complex quartz overgrowth with large frosty tabular inclusions in upper right.
06898830015831917011324.jpg
Flat, complex quartz overgrowth with embedded pocket breccia clasts.
05267410015831917003441.jpg
Complex quartz overgrowth with large frosty tabular inclusions in upper right.
06898830015831917011324.jpg
Flat, complex quartz overgrowth with embedded pocket breccia clasts.
05267410015831917003441.jpg
Complex quartz overgrowth with large frosty tabular inclusions in upper right.
01150710015831917024833.jpg
Flat, complex quartz overgrowth with embedded pocket breccia clasts.
03181960015831917026730.jpg
Blocky distorted quartz overgrowth with flabellate inclusions.
04688730015853162102260.jpg
Large rough quartz encrusted by secondary mineralization and chock-full of tabular, flabellate inclusions.
09934490015520047245588.jpg
Blocky distorted quartz overgrowth with flabellate inclusions.
04688730015853162102260.jpg
Large rough quartz encrusted by secondary mineralization and chock-full of tabular, flabellate inclusions.
09934490015520047245588.jpg
Blocky distorted quartz overgrowth with flabellate inclusions.
04688730015853162102260.jpg
Large rough quartz encrusted by secondary mineralization and chock-full of tabular, flabellate inclusions.
02241320015853133902829.jpg
Flat quartz crystal with embedded pocket breccia clasts and chock-full of tabular inclusions.
09255620015853162109637.jpg
Close-up of inclusions in the crystal at left.
04306640015853132493730.jpg
Flat quartz crystal with embedded pocket breccia clasts and chock-full of tabular inclusions.
09255620015853162109637.jpg
Close-up of inclusions in the crystal at left.
03755810015853162112389.jpg
Flat quartz crystal with embedded pocket breccia clasts and chock-full of tabular inclusions.
06934770015853162111332.jpg
Close-up of inclusions in the crystal at left.
07664300015831922953441.jpg
Smaller, "normal" undistorted quartz crystal filled with randomly oriented inclusions.
02310330015851941507696.jpg
Close-up of a 3.5 cm-long inclusion, showing partial filling with a very fine-grained mineral resembling secondary albite. The alignment of grains suggests that the original crystals were longitudinally striated and had a rectangular outline.
03391290015582264036935.jpg
Smaller, "normal" undistorted quartz crystal filled with randomly oriented inclusions.
02310330015851941507696.jpg
Close-up of a 3.5 cm-long inclusion, showing partial filling with a very fine-grained mineral resembling secondary albite. The alignment of grains suggests that the original crystals were longitudinally striated and had a rectangular outline.
07664300015831922953441.jpg
Smaller, "normal" undistorted quartz crystal filled with randomly oriented inclusions.
08705370015851941505733.jpg
Close-up of a 3.5 cm-long inclusion, showing partial filling with a very fine-grained mineral resembling secondary albite. The alignment of grains suggests that the original crystals were longitudinally striated and had a rectangular outline.


Given their abundance, I found it odd that very few old specimen labels attempt to identify these inclusions. Despite prolific collector and author Richard Schooner having written several articles about the state's, the region's, and the Strickland pegmatite's mineralogy (see reference list on Strickland pegmatite mindat.org page), he never mentioned them. Neither did many other writers. Maybe because no one had a clue to their identity, they left them for someone else to figure out, which I also did for decades. I could find only one mention of them in the literature, by Peter Zodac in 1937[1]:

A number of large, loose crystals, some at least one foot long, were found September 8, 1935, by Messrs. R. Emmet Doherty of Peekskill, and Henry Thurston of Montrose, N. Y. The crystals were of good quality but partly stained by brown limonite; some of the crystals were coated by a secondary growth of minute drusy quartz crystals, also stained brown by limonite. The surfaces of these large crystals resembled sandpaper in texture. One pale smoky crystal, unfortunately broken, 3 inches long, 2 inches wide, and 1 inch thick, whose edges were stained by limonite, contained a large number of white, slender inclusions which were assumed to be albite. The inclusions took all forms—one resembled a miniature mineral hammer; others formed letters of the alphabet as K, V, X, M, T, U, L.


On one old label, the inclusions are called bismutite after bismuthinite. This was not unreasonable, given that bismuthinite is known from area pegmatites, can form acicular crystals, and is commonly altered to nonmetallic, light-colored, earthy to waxy secondary Bi minerals. But these bismuth minerals have not been confirmed in the Strickland pegmatite, and they are rare in other Connecticut pegmatites and not present in their cleavelandite-rich zones. I took a close, microscopic look at several of the mystery inclusions, examining spots where they reach a host crystal's surface, and I found that they vary from hollow to partially or completely filled with an extremely fine-grained, white to tan mineral beyond the microscope's resolution, but that appear to be similar to the fine-grained secondary albite found in, on, and around the quartz crystals. They do not resemble any secondary bismuth mineral, especially since many of them are hollow. What they do resemble, however, are the molds of elongated, tabular crystals that were later partially or completely filled with something. Partially filled voids show alignment of secondary grains, indicative of longitudinal striations on the original crystals. Perusing mindat.org, I found some hambergite crystal photgraphs that look like they could be a match for the original mineral, but many of them have terminations different from the voids seen here, and they seem to occur in pockets as individual crystals rather than in groups. Whatever mineral this was, it clearly preferred to crystallize late in the mineral sequence after pocket collapse and at moderately low temperature (being found only in pocket quartz and not matrix quartz; and being unbroken and clearly secondary), was very common (being enclosed in so many quartz crystals), and then shortly afterwards dissolved away, both inside and outside (or so I thought) of the quartz hosts.

05205380015832060479624.jpg
Metallic bismuthinite crystals in quartz from a small pegmatite in Haddam, Connecticut.
01502250015832060485340.jpg
Although some local bismuthinite is acicular, much of it occurs in massive aggregates like this one from the Simpson Quarry. It occurs in rare, isolated masses frozen in matrix, not in miarolitic cavities.
05205380015832060479624.jpg
Metallic bismuthinite crystals in quartz from a small pegmatite in Haddam, Connecticut.
06719780015721136384078.jpg
Although some local bismuthinite is acicular, much of it occurs in massive aggregates like this one from the Simpson Quarry. It occurs in rare, isolated masses frozen in matrix, not in miarolitic cavities.
05696940015664248895901.jpg
Metallic bismuthinite crystals in quartz from a small pegmatite in Haddam, Connecticut.
01502250015832060485340.jpg
Although some local bismuthinite is acicular, much of it occurs in massive aggregates like this one from the Simpson Quarry. It occurs in rare, isolated masses frozen in matrix, not in miarolitic cavities.
06260210015832060483441.jpg
Bismutite after bismuthinite from the Hewitt Gem Quarry in Haddam, Connecticut. FOV is 3.5 cm.
00129940015832060491324.jpg
Another bismutite after bismuthinite from the Case Quarries in Portland, Connecticut. These pseudomorphs really do not resemble those found in the Strickland quartz crystals. FOV is 22 mm.
04271230015672920541777.jpg
Bismutite after bismuthinite from the Hewitt Gem Quarry in Haddam, Connecticut. FOV is 3.5 cm.
00129940015832060491324.jpg
Another bismutite after bismuthinite from the Case Quarries in Portland, Connecticut. These pseudomorphs really do not resemble those found in the Strickland quartz crystals. FOV is 22 mm.
03173130015667957066004.jpg
Bismutite after bismuthinite from the Hewitt Gem Quarry in Haddam, Connecticut. FOV is 3.5 cm.
00129940015832060491324.jpg
Another bismutite after bismuthinite from the Case Quarries in Portland, Connecticut. These pseudomorphs really do not resemble those found in the Strickland quartz crystals. FOV is 22 mm.
05298510015023151644100.jpg
A hambegite crystal resembling the voids in Strickland quartz crystals. But are these too thick?
07417580014946650762131.jpg
A hambergite crystal very unlike the voids.
07286740014947466577708.jpg
A hambegite crystal resembling the voids in Strickland quartz crystals. But are these too thick?
07417580014946650762131.jpg
A hambergite crystal very unlike the voids.
05298510015023151644100.jpg
A hambegite crystal resembling the voids in Strickland quartz crystals. But are these too thick?
07417580014946650762131.jpg
A hambergite crystal very unlike the voids.


BLADED EPIMORPHS IN THE CAVITIES

Very rare from here are miarolitic cavity specimens that show rough-surfaced, columnar albite epimorphs with a hollow, tabular interior (within masses of secondary, fine-grained albite). Even rarer are similar hollow epimorphs with an extremely fine-grained, smooth surface instead. The size, shape, and general character of these rare, hollow epimorphs are very similar to the quartz hosted voids described above. An SEM-EDS analysis of the latter type gave a close match for K-feldspar. It seems that some of the mystery inclusions were preserved outside of the quartz as epimorphs consisting of albite or adularia (low-temperature K-feldspar). I have not been able to obtain a sample of the mineral inside the quartz inclusions, but visually it looks very similar to the epimorphing adularia. Regardless, none of these represent the original mystery mineral.

00895820015853162124715.jpg
Secondary fine-grained albite filling a collapsed miarolitic pocket, with secondary purple fluorapatite and quartz, including rare, elongated, hollow epimorphs.
06219470015853162134507.jpg
Close-up of the elongated, albite epimorphs, FOV is 3 cm.
00895820015853162124715.jpg
Secondary fine-grained albite filling a collapsed miarolitic pocket, with secondary purple fluorapatite and quartz, including rare, elongated, hollow epimorphs.
06219470015853162134507.jpg
Close-up of the elongated, albite epimorphs, FOV is 3 cm.
00895820015853162124715.jpg
Secondary fine-grained albite filling a collapsed miarolitic pocket, with secondary purple fluorapatite and quartz, including rare, elongated, hollow epimorphs.
06219470015853162134507.jpg
Close-up of the elongated, albite epimorphs, FOV is 3 cm.
08694880015853162145126.jpg
Very rare tabular epimorphs, mostly broken open lengthwise. FOV is 6 mm.
00408680015853162166297.jpg
Relatively smooth-surfaced, hollow epimorphs. FOV is 6 mm.
08694880015853162145126.jpg
Very rare tabular epimorphs, mostly broken open lengthwise. FOV is 6 mm.
00408680015853162166297.jpg
Relatively smooth-surfaced, hollow epimorphs. FOV is 6 mm.
08694880015853162145126.jpg
Very rare tabular epimorphs, mostly broken open lengthwise. FOV is 6 mm.
00408680015853162166297.jpg
Relatively smooth-surfaced, hollow epimorphs. FOV is 6 mm.
02730160015831938509624.jpg
SEM-EDS spectrum of epimorphs shown above, results are consistent with K-feldspar — adularia.


THE PROPOSED CULPRIT — BIKITAITE

For a long time, I would occasionally think about this mystery mineral while looking through books on pegmatites, examining pegmatite specimens, or perusing mindat.org images. They were always back there in my brain, but nothing looked right until I came across a possibile match one day while casually browsing through the Collector's Guide to the Zeolite Group by Robert J. Lauf. There are many zeolite species in Connecticut; they occur in a variety of relatively low-temperature, mineral-forming geo-environments, and I am very familiar with most of them. I usually think of zeolites as occurring in low-temperature contexts, such as vesicles and fractures in basalt and gneiss, and I hadn't considered their possible occurrence in pegmatites, even though I knew there are higher-temperature zeolites like pollucite in some pegmatites, though they are very rare. The photographer in me was just mentally critiquing the pictures in the book when I unexpectedly came upon photos of bikitaite, which is, as I soon learned, among the rarest of pegmatite zeolites (with just four mindat.org localities listed). The photographs of pseudo-orthorhombic bikitaite crystals from the Bikita pegmatite, Zimbabwe, and the Foote lithia mine, North Carolina, USA, are dead ringers for the shape, size, and striations of the mystery inclusions in the large Strickland quartz crystals!

08548320015832060492894.jpg
Bladed, rectangular, striated bikitaite crystals from the Foote lithia mine, North Carolina.
03136550015832060503229.jpg
Bikitaite crystals with a fluorapatite crystal, both partially encrusted with a very fine-grained mineral like the epimorphs shown above.
02352410014977593181087.jpg
Bladed, rectangular, striated bikitaite crystals from the Foote lithia mine, North Carolina.
05286050014977599516929.jpg
Bikitaite crystals with a fluorapatite crystal, both partially encrusted with a very fine-grained mineral like the epimorphs shown above.
02352410014977593181087.jpg
Bladed, rectangular, striated bikitaite crystals from the Foote lithia mine, North Carolina.
05286050014977599516929.jpg
Bikitaite crystals with a fluorapatite crystal, both partially encrusted with a very fine-grained mineral like the epimorphs shown above.
04418440014977196225449.jpg
A jackstraw pile of bikitaite crystals from the Foote mine.
07387870015832060519471.jpg
Bladed, rectangular, striated, partially encrusted bikitaite crystals from the Bikita pegmatite, Zimbabwe.
04418440014977196225449.jpg
A jackstraw pile of bikitaite crystals from the Foote mine.
00668510014977200167757.jpg
Bladed, rectangular, striated, partially encrusted bikitaite crystals from the Bikita pegmatite, Zimbabwe.
04418440014977196225449.jpg
A jackstraw pile of bikitaite crystals from the Foote mine.
00668510014977200167757.jpg
Bladed, rectangular, striated, partially encrusted bikitaite crystals from the Bikita pegmatite, Zimbabwe.


The Bikita and Foote localities are very chemically evolved, Li-rich pegmatites with many secondary minerals formed by the alteration of spodumene and lithiophilite. Spodumene, and to a much lesser extent lithiophilite, are abundant in the Strickland pegmatite's cleavelandite-quartz zone, as are minerals resulting from their alteration. The late-stage alteration of these lithium minerals is well known (both phenomena were first described from the Fillow pegmatite in the late 19th century) and involves the loss of very mobile Li from these primary minerals. With the alteration of much of this zone's spodumene and lithiophilite, there was certainly available Li in solution following pocket collapse at the Strickland pegmatite. Most telling is that bikitaite is a Li zeolite, very similar in composition to albite (if you take out the Li and water) and K-feldspar (take out the water and substitute K for Li). Pseudomorphing minerals typically have a similar chemistry to the original ones, and albite and K-feldspar do form from the alteration of spodumene at the Fillow quarry and elsewhere. The bladed, pocket bikitaite crystals are clearly secondary and late in the overall pegmatite mineral sequence.

Bikitaite's temperature of crystallization is apparently higher than stilbite, which Tschernich[2] reports as occurring up to 200°C. Primary pegmatite mineral crystallization, from wall zone to miarolitic pocket wall, ranges from about 450°C to 350°C[3]. So bikitaite likely crystallizes between 350°C and 200°C. But this is still early enough in the sequence of pocket crystallization that bikitaite is potentially subjected to dissolution from later changes in hydrothermal solutions, which is probably something that makes bikitaite so rare.

Similar inclusions have not been found in the other four Connecticut pegmatites with abundant Li, miarolitic cavities, and associated quartz crystals, particularly the Fillow and Gillette pegmatites. Whether their absence is due to never having crystallized or through lack of preservation is unknown, but of these, only the Fillow pegmatite has Li-rich, primary mineralization showing substantial alteration (lithiophilite and spodumene) that provides a source for secondary Li mineralization; the others have Li mostly in stable elbaite and micas. Cavities in the Gillette pegmatite are rife with quartz crystals, many with inclusions of the fibrous muscovite variety schernikite. These crystals are still extant, both internally and externally to quartz, and have a very different character (long fibers with rhombic cross-sections) than Strickland's quartz inclusions and so do not explain them. Schernikite is very uncommon at Strickland and does not occur there as inclusions.

06734140015833590989624.jpg
Smoky quartz crystals from a miarolitic pocket at the Gillette pegmatite in Haddam, Connecticut. Muscovite variety schernikite occurs as both individual fibers included in the quartz and as parallel growth bundles.
02279200015855259005666.jpg
Close-up of the included schernikite fibers at left. The inclusions are extant, not hollow voids and have a rhombic cross-section. They are not terminated by crystal faces but by perfect cleavage perpendicular to the c-axis like any mica. FOV is 15 mm.
06734140015833590989624.jpg
Smoky quartz crystals from a miarolitic pocket at the Gillette pegmatite in Haddam, Connecticut. Muscovite variety schernikite occurs as both individual fibers included in the quartz and as parallel growth bundles.
02279200015855259005666.jpg
Close-up of the included schernikite fibers at left. The inclusions are extant, not hollow voids and have a rhombic cross-section. They are not terminated by crystal faces but by perfect cleavage perpendicular to the c-axis like any mica. FOV is 15 mm.
06734140015833590989624.jpg
Smoky quartz crystals from a miarolitic pocket at the Gillette pegmatite in Haddam, Connecticut. Muscovite variety schernikite occurs as both individual fibers included in the quartz and as parallel growth bundles.
02279200015855259005666.jpg
Close-up of the included schernikite fibers at left. The inclusions are extant, not hollow voids and have a rhombic cross-section. They are not terminated by crystal faces but by perfect cleavage perpendicular to the c-axis like any mica. FOV is 15 mm.


At Strickland, the predominant hydrothermal pocket solutions apparently had a neutral pH[4], because the abundant bertrandite forms from the dissolution of beryl under those conditions. Low pH solutions produce bertrandite, too, but also phenakite and euclase. The latter two are very rare here, and the few crystals found are etched. These findings suggest that the solutions started out with low pH but then went to neutral. Perhaps this change is what took away the bikitaite, leaving only voids in quartz and epimorphs to show that the mineral was ever there.

01118890015833587829624.jpg
Very rare, etched prismatic phenakite crystal with tabular bertrandite and tan albite. FOV is 4 mm.
02064140015853162171401.jpg
Very rare, etched potential euclase crystals with secondary quartz and cookeite encrusting a large quartz crystal. FOV is 15 mm.
01118890015833587829624.jpg
Very rare, etched prismatic phenakite crystal with tabular bertrandite and tan albite. FOV is 4 mm.
02064140015853162171401.jpg
Very rare, etched potential euclase crystals with secondary quartz and cookeite encrusting a large quartz crystal. FOV is 15 mm.
01118890015833587829624.jpg
Very rare, etched prismatic phenakite crystal with tabular bertrandite and tan albite. FOV is 4 mm.
02064140015853162171401.jpg
Very rare, etched potential euclase crystals with secondary quartz and cookeite encrusting a large quartz crystal. FOV is 15 mm.


CONCLUSION

I believe bikitaite is the most probable solution to the question of the identity of the original mineral, but I acknowledge that the evidence so far is circumstantial and has not been proven. Another, less likely, possibility is hambergite, but I admit I do not know much about this mineral. It seems to be a primary rather than secondary species (comments about this would be appreciated). Unless an actual crystal of the precursor mineral is found, which I consider to be very unlikely because the quarrying is long over and so many pieces have already been collected, there is nothing to analyze. It's possible, of course, that these inclusions were formed by a mineral still unknown to science, but lacking a better alternative among presently known species, bikitaite seems the likeliest possibility. I have not added bikitaite as a species to the Strickland pegmatite page yet; because of its rarity, I would first like to get more feedback, so please comment. I welcome your input.

REFERENCES

1. Zodac, Peter (1937) Minerals of the Strickland Quarry. Rocks & Minerals: 12: 131-144.

2. Tschernich, Rudy. (1992), Zeolites of the World. Geoscience Press, Phoenix.

3. London, David. (2008), Pegmatites. The Canadian Mineralogist Special Publication 10: 243.

4. Simmons, William B., et al. (2003), Pegmatology. Rubellite Press, New Orleans: 84.




Article has been viewed at least 685 times.

Discuss this Article

19th Mar 2020 15:00 GMTRichard Gunter Expert

Hi Harold:

Good article. In my investigations of the Tanco Secondaries I found bladed epimorphs of  Fluorapatite that are very similar in size and shape to your Adularia epimorphs. You can see an example in my Fluorapatite-Wopmayite sample photo post from Tanco. I had not thought of Bikitaite as a possible precursor; though the Tanco pegmatite is lithium-rich.

19th Mar 2020 16:15 GMTHarold Moritz Expert

Hi Richard:
Thanks for the comment. Can you please post a link to the photo you refer to, not sure I could find it, I didnt see any epimorph photos. However, I assume that the fluorapatite crystals will have hexagonal cross-sections (unless distorted) and thus would not match the thin, rectangular cross-sections of the Strickland voids. Assuming they are distorted fluroapatite at Tanco and they are the culprit at Strickland, how would all the thousands of such crystals get a similar, consistent distortion at Strickland? Also, there is no such habit for fluorapatite at Strickland and plenty of undissolved, pristine, tabular to short crystals preserved there. My understanding is that fluorapatite is very stable and I've never seen any etched or replaced crystals of that mineral.

19th Mar 2020 16:06 GMTDonald B Peck Expert

Hi Harold,

Enjoyed reading your article.  Well done!  Back in the '50s and early '60s I lived in Connecticut and spent a lot of hours at Strickland.  

Don

19th Mar 2020 16:46 GMTRichard Gunter Expert

Hi Harold:

The photo in question is:

<pic id='427912' width=600></pic>

The epimorph is the aggregate of brown hydroxyapatite in the lower centre of the photograph, surrounding a platy cavity left by a prismatic mineral.

Flourapatite at Tanco is a primary mineral, often manganoan and green coloured. The late-stage hydrothermal fluids re-mobilize the primary Fluorapatite into a brown carbonate apatite ( pictured in the photograph) and a radial pink carbonate apatite. The epimorphs only occur in the brown carbonate apatite. The brown carbonate apatite is also the only one to occur with Quartz crystals. The radial pink carbonate apatite occurs with the Lithiophosphate paragenesis.

19th Mar 2020 16:49 GMTRichard Gunter Expert

Opps that did not post my photo. I will have to find out how and repost.

19th Mar 2020 17:35 GMTHarold Moritz Expert

Use insert item, select mindat photo, and enter the photo number, I did it based on your earlier post.
Now that I've seen the pix, I was very confused by your earlier comments, I thought the apatite was the mineral that left the void, instead it is the epimorphing mineral. Yes, the voids do look like the tabular habit of bikitaite.

19th Mar 2020 18:06 GMTRichard Gunter Expert

Hi Harold:

I will know how to insert next time, thank you. As far as I know Bikitaite has not been noted as a secondary phase at Tanco. I guess it is all gone now in the hydrothermal alteration. Some of the epimorphs were quite large (2 to 3 cm) so there must have been some interesting Bikitaite crystals at one time.

Regards,

Richard Gunter

20th Mar 2020 04:55 GMTKeith Compton Manager

Harold

Nice article.
I'm no mineralogist by any means but the article appears well reasoned.
Bikitaite is certainly not exactly a common mineral and most would not consider this as a possibility.
It is certainly associated with pegmatites - you only need look at the Foot Lithium Co. Mine.

One of your author references - Peter Zodac (1937) - would not have considered it, as the mineral was not named until 1957.

Well done ... and great photos too.

20th Mar 2020 10:05 GMTJohan Kjellman Expert

From your description it sounds like the inclusions in quartz may be the best bet to find at least traces of the primary mineral in an unaltered state . 
Why not send some of these quartz crystals to some pegmatite oriented researcher with the instrumental resources and theoretical capabilities of formulating a problem for an undergraduate study. I am thinking directly of David London. 

cheers

20th Mar 2020 13:26 GMTHarold Moritz Expert

Thank you all for the comments. My hope is that this may result in others taking a critical look at Li-rich pegmatite pocket assemblages for other potential bikitaite localities, which it already has. Even if it is dissolved away, it is still a locality. I have thought about trying to find some existing material in one of the quartz crystals, the problem is how many and which ones would have to be destroyed in the search? I doubt one could tell visually from the outside, I havent seen anything that would lead me to believe a certain inclusion has original material, and most are fairly deep inside. Because the quarry is long inactive and dumps gone each crystal has value that I dont want to lose. Perhaps if someone is interested and can work on them without wrecking them they can reply here with a proposed method.

I reviewed all the Strickland literature and was surprised that only Zodac mentions them but made no guess. Schooner was such a keen observer, chronicler and (to a fault IMO) speculator that the absence of any text on the subject is puzzling. But then he (and others) missed identifying wodginite as a new mineral that they collected here before it was described from elsewhere years later.

20th Mar 2020 20:19 GMTRalph Bottrill Manager

Interesting article, but would be nice to look for inclusions of the mystery mineral in quartz and analyse them. You may need something like LA-ICPMS as EDS and Electron microprobe cannot do Li.

25th Mar 2020 16:04 GMTTony Albini

Fritz, I do not know if you received my email yesterday.  A later manuscript of Richard Schooner mentions analytical work on what he says was closest to bikitaite, also i have a thumbnail specimen from his collection that he labelled bikitaite. Micro xls in quartz and albite, since you did this great research YOU should add bikitaite to the Strickland quarry list.

26th Mar 2020 15:31 GMTHarold Moritz Expert

Thanks, well, the only written mention of bikitaite from any Schooner document I have is from the unpublished, undated manuscript on central Connecticut minerals written circa 1990 (the latest date in it is 1988). The paragraph on bikitaite is a bit vague but seems to be talking about material analyzed from the Walden Gem Quarry:

"A few specimens of pollucite, from the Walden gem mine, contain warped layers of a hard columnar white mineral, closely resembling eucryptite. As with identical material from the Strickland quarry, also with pollucite, the X-ray pattern indicates spodumene; perhaps pseudomorphous after the mineral it had originally replaced. The surfaces of the layers show a softer white mineral, in aggregated tabular crystals, all very little. The X-ray pattern is close to bikitaite."

This paragraph unfortunately does not confirm bikitaite at either Walden or Strickland, especially without inclusion of the original analytical data, which is why I did not mention it in the article. (I recently had EDS done on what I think is similar, splintery material from Walden that best matched spodumene, but difficult to say if it is exactly the material he refers to, but that is another matter. See that mindat locality for pix and EDS reports.)

Schooner also wrote an unpublished, undated manuscript about Strickland minerals sometime in the late 1980s or early 1990s - the latest date in it is 1987. It does not mention bikitaite. I did not include it in the Strickland references because it is not generally available.

Considering the rarity of this mineral so far, to add it to the locality I think a modern analysis with photodocumentation and accompanying analytical report is needed.

27th Mar 2020 15:59 GMTTony Albini

Fritz, I have all of Dick's manuscripts.  My copy of his latest has additional information verbally obtained from Dick in our discussions, I added all this material to my copy on various new finds. He was supposed to publish again but it never happened. However, he would continually look at his XRD charts so I believe he later came to the conclusion that the material was bikitaite.  He was very finicky on his interpretation of the data.  The xrd charts were bought by Bob Whitmore, you may want to contact him to see if he still has them.
 
Mineral and/or Locality  
Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization. Public Relations by Blytheweigh.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2020, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters.
Privacy Policy - Terms & Conditions - Contact Us Current server date and time: April 9, 2020 01:37:15
Go to top of page