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The Minerals of the Red Hill Granites, Isle of Skye

Last Updated: 14th Apr 2013

By Steve Rust

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Relief Map of the Isle of Skye Showing the Location of the Volcanic Central Complex in red



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Waterfall at Eas a Bradain


The Isle of Skye Volcanic Complex occupies the central area of the Isle of Sky, Inner Hebrides, NW Scotland, a well studied geological, and petrological area. The first comprehensive study was undertaken by A. Harker published in 1904 followed by several papers by other authors over the intervening years. This article will deal with the minerals from some of the Red Hill Granites. To date there are thought to be 16 known small granitic intrusions comprising the Red Hills. A possible 17th is found between the Loch Ainort and Glas Beinn Mhor Granites, with another 2 undefined granite's with in the complex. The oldest recorded Tertiary Granite is the Coire Uaigneich, which is a ribbon like structure west of the Sligahan River. (an attempt was made to reach this area but horizontal rain put a stop to that). A feature of many of the granites on Skye are the abundant miarolitic cavities, having been recorded to 15cms on Marsco. Although field observations show that most of the cavities measure to no more than 6cm; miarolitic cavities at this end of the size scale are rare. Investigations (1997-to date)of seven of the granites has shown a number of euhedral micro minerals associated are with the cavities; including excellent micro crystals of zircon, fluorite, epidote, allanite-(Ce), gadolinite-(Y), kainosite-(Y), hedenbergite, quartz, K-feldspar; as well as late stage zeolites stilbite-Ca, chabazite-Ca. Work by A.G.Tindell (2008) has thrown further light on the complex zoned nature of some Pyroxenes/Amphiboles in the Skye granites. Although this article does not differentiate to any extent the various zoned nature of the Pyroxenes/Amphiboles. A number of species have been recorded in early petrological papers with no real description of the euhedral appearance of the crystals for the mineral collector. A number of other granites with in the complex have been investigated mostly north (Northern Porphyritic Felsite) and just west of Glamiag (Southern Porphyritic Granite) but most of the cavities are completely filled with a Chlorite or less than 1cm in diameter, and warrent fether investigation.

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The Black Basic-Ultra-basic Cuillins on the west and the Red Cuillins Acid Granite on the east. The Sligachan River can be seen meandering its way through the Glacial formed Valley. Looking from the south


It was some years ago while reading the Excursion Guide To The Geology Of The Isle Of Skye by B.R.Bell & J.W.Harris (1986) that prompted me to not go rushing off to the many zeolite locations on the island in 1997 (which I had done before this date).
All of the minerals described and collected have been found in glacial corries, small road side quarrys, at the edges of old marble quarrys, and from road development work. This study also entailed the investigation of the exposed granite on the flanks and summits of the Red Hills. It would appear that these later areas have not been subjected to aggressive glacial ice flow, as have the corries, or erosion by river or tidal flow, so that large areas on the Red Hills appear to have not been stripped back to reveal ‘fresh’ granite. Exposed granites on the summits or flanks have been very badly weathered over a long period of time. The result is that many of the minerals have been etched or are completely absent from the miarolitic cavities. The cavities may also contain a sand of some of the minerals which once adhered to cavity sides; while many of the cavities are completely iron oxide stained from the break down of iron bearing mineral species. Work on the minerals from the granites is continuing weather and time permitting.

The minerals collected in this study are from the Loch Ainort, Glas Beinn Mhor, Glamaig, Marsco, Beinn na Caillich Granites, and the Beinn an Dubhaich granite the most southerly, fair cross-section of the Red Hill granites on Skye. An unnamed intrusion seen in Loch Ainort at high and low tide level has also been collected from, but it dose not appear to have been named by the early literature. The outcrop is textually different (containing quite large anhedral to euhedral Pyroxene crystals to 3cm) from either the Loch Ainort, or the Glas Beinn Mhor granites, which it appears to lay between. It was also noted in this study that blocks of the Beinn an Dubhaich Granite have areas of fine grain textured 'Felsite' which can pass rapidly into a net work of narrow none persistent pegmatite veinlets to 10cm long by <1cm wide, many of the other studied granites show no gradation. At some time in the future it is envisaged that a start will be made on the Riebeckite bearing granites west of the Sligahan River.

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A veiw of the Red Cuillins Central Skye Volcanic Complex, Looking southward





Geology.
The Isle of Skye Volcanic Central Complex constitutes part of the British Tertiary Igneous Province (BTIP) having been proved from Lundy Island off the Atlantic coast of Devon stretching intermittently northward to St.Kilder a distance of 1000Km. The BTIP constitutes the oldest southern extension of a Igneous complex that extents to the southern Greenland coast, and Iceland the youngest, and is collectively called the North Atlantic Igneous Province.

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Beryl Lundy Island 0.5cm long crystal
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Topaz Diamond Rocks N.I 0.5cm high crystal
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Beryl Lundy Island 0.5cm long crystal
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Topaz Diamond Rocks N.I 0.5cm high crystal
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Beryl Lundy Island 0.5cm long crystal
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Topaz Diamond Rocks N.I 0.5cm high crystal



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Magnetite Isle of Mull crystals to 0.5mm


Volcanism on Skye is thought to be associated with late movement on the Jurassic-Cretaceous Camasumnary fault crosses NE-SW in the south of the Isle associated with crustal spreading. The igneous activity starting about 55my ago and to have lasted off and on for about 7my uplifting and the crust by an estimated 2Km. The volcanic area of the Skye Central Complex is composed of two main rock types, on the west side are basic to ultrabasic rocks like Gabbros, Peridotites, and Dunnites forming the craggy Black Cuillins. Largely west of the Sligachan River are the rounded acid-granite hills, historically called the West and East Red Hills. A feature of the granites on Skye is the partial mixing of the granite magmas with basic magmas forming hybrid rock types; for instance the so-called Glamagite and Marscoite hybrid granites. The mixing of the basic and granite magmas has added greatly to the variety of minerals that are found in the miarolitic cavities. Pressure and melt studies on the granite's indicates that they formed at a depth of about 1-1.5km. The lighter granite magma's floating on top of the basic magma; which is estimate to reach a depth of 16Km, with a cylindrical like shape. The granites having intruded relatively high in the crust the pressure would have been reduced allowing gas along with super heated hydrothermal water to form bubbles in the granitic magma leading to the formation of pegmatitic miarolitic cavities. Nearly all of the granites are partial segments of ring like intrusions believed to be a consequence of rocking-like motion in the Isle of Skye Complex; the granites intruded one side then the other. The exception appears to be the Beinn na Caillich granite which has a more circular pluton-like shape. The Beinn an Dubhaich the most southerly granite intrusion on Skye was intruded in to Cambrian limestone. The result of the granite's intrusion has metamorphosed the limestone in to a marble, and leading to the formation of the well known Cal-silicate Skarns mostly west of Torrin village, Isle of Skye, Tilley (1951).


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Geological Map of the Red Hill Granites



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Bealach nam Mulachag with Beinn na Caillich Red Cuillin Hills. Looking nortward
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Glamaig Red Cuillin. Looking southward
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Marsco red Cuillin. Looking Southward
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Bealach nam Mulachag with Beinn na Caillich Red Cuillin Hills. Looking nortward
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Glamaig Red Cuillin. Looking southward
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Marsco red Cuillin. Looking Southward
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Bealach nam Mulachag with Beinn na Caillich Red Cuillin Hills. Looking nortward
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Glamaig Red Cuillin. Looking southward
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Marsco red Cuillin. Looking Southward
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Glas Beinn Mhor Ridge Granite. Looking Eastward
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Collecting Miarolitic Granite on the Shore of Loch Ainort
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Marble Quarries surrounded by the Beinn an Dubhaich Granite. Looking southward
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Glas Beinn Mhor Ridge Granite. Looking Eastward
03991700014946297747713.jpg
Collecting Miarolitic Granite on the Shore of Loch Ainort
06926680014960939606230.jpg
Marble Quarries surrounded by the Beinn an Dubhaich Granite. Looking southward
04570480014960939607552.jpg
Glas Beinn Mhor Ridge Granite. Looking Eastward
03991700014946297747713.jpg
Collecting Miarolitic Granite on the Shore of Loch Ainort
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Marble Quarries surrounded by the Beinn an Dubhaich Granite. Looking southward


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Zircon 1mm crystals



Minerals.

Allanite-(Ce) has been found in crystals from some of the Skye granites in this study; forming very good bladed and tabular dark brown crystals measuring to 4mm from the Beinn an Dubhaich granite's, as single tabular crystals to 1mm from the Glas Beinn Mhor and Loch Ainort granites. Allanite-(Ce) has not been seen in crystals in this study from the other granites, but petrological studys confirm the presents of allanite. There is a tiny amount of allanite-(Y) in association with the crystals of allanite-(Ce) in a specimen analysed from the Beinn an Dubhaich granite (Priv Com Pavel Kartashov).

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Allenite-(Ce)3mm crystal
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Allenite-(Ce)1mm crystal
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Allenite-(Ce)3mm crystal
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Allenite-(Ce)1mm crystal
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Allenite-(Ce)3mm crystal
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Allenite-(Ce)1mm crystal



Anatase was very rarely found on a hand full of specimens from the Beinn an Dubhaich granite, were it forms typical black double terminated crystals to 0.5mm. From the same granite anatase is seen as light honey yellow tabular crystal 0.1mm as a replacement of Titanite crystals. Anatase was found on at-least two specimens from the Loch Ainort granite, as tiny black 0.15mm double terminated steep pyramidal crystals on clinochlore.

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Anatase crystals to 0.4mm




Almandine Recorded from the Southern Porphyritic Granite, Thompson(1969)

Apophyllite is a rear late stage zeolite related mineral in the Skye granite's, forming colourless lustrous crystal groups measuring to 5mm. Occasionally forming double terminated crystals to 1.5mm long with strong development of the prism and pyramid faces.

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Apophyllite 1mm long crystal



Augite Recorded from the Glamaig granite Tindle (2008) in thin section

Biotite a major constituent of all the Skye granites, forming rounded book-like crystals to 8mm diameter; also commonly elongated parallel to the 'C' axis measuring to 1cm tall. The biotite colour is from black to translucent green on thin crystal leaves. The biotite crystals are commonly encased by a druse of green to clove brown clinochlore.

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Biotite 4mm wide group
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Biotite 3mm wide group
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Biotite 4mm wide group
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Biotite 3mm wide group
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Biotite 4mm wide group
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Biotite 3mm wide group



Calcite an uncommon late stage mineral as incomplete thin platy crystals spanning miarolitic cavities to 1cm some times coated by minute crystals of titanite. Also as tabular translucent white pseudohexagonal crystals to 1.5mm; very rarely found as prismatic crystals in small clusters to 3mm.

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Calcite 1mm group
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Calcite 1.5mm crystal
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Calcite 1mm group
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Calcite 1.5mm crystal
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Calcite 1mm group
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Calcite 1.5mm crystal
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Calcite 2mm wide crystal group




Chevkinite-Ce Yet to be confirmed in euhedral crystals; seen as elongated black prismatic crystals embedded in the granite to 1mm long causing reddish alteration halos in the K-feldspar, recorded by Exley (1980)and described as sphenes with 46% RE oxides from Skye granites and he comments that they are petrographically similar to allanite; further investigation has indicated their composition is similar to the chevkinite's, and see Tindle (2008)

Chabazite-Ca so far only found in the Glas Bheinn Mhor granite, but even in this granite only rarely; chabazite-Ca has been found as a single colourless 1.5mm crystals. Some what more abundant as orange sharply formed single crystals with a pseudocubic appearance, and as small inter-grown groups of 3 or 4 crystals; individual crystals measuring to 4mm on edge. Chabazite-Ca is a late stage mineral in the miarolitic cavities associated with Stilbite-Ca,and Prehnite.

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Chabazite-Ca 2mm crystal group
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Chabazite-Ca 1mm crystal
05318730014947273587771.jpg
Chabazite-Ca 2mm crystal group
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Chabazite-Ca 1mm crystal
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Chabazite-Ca 2mm crystal group
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Chabazite-Ca 1mm crystal
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Chabazite-Ca 1mm crystal




Clinchlore a common minerals in all the granite investigated were it is commonly the result of the brake down of Mg-Fe-Al Silicates, and as replacement of titanite crystals from the Beinn an Dubhaich granite. Clinochlore crystals are noted to be very thin platy with raged edges to a flaky appearance; mostly of deep brown colour due to alteration. A light grey-green chlorite was found on a small number of specimens with a pearly luster.

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Clinochlore. 4mm crystal spray


Epidote is fairly abundant in the granites were it forms prismatic to almost tabular crystals to no more than 1.5mm long, occasionally double terminated. Many of the epidote crystals have deep brown sharply defined opaque central areas; the crystals rapidly changing to a clear yellowish colouration. Epidote is later than the pyroxenes, sometimes forming sparkling yellow green tiny prismatic crystals over-grown on acicular pyroxene crystals from the Bhienn Glas Mhor granite.

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Epidote. 0.6mm tall crystal
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Epidote crystals on a 3mm Pyroxene crystal
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Epidote. 0.6mm tall crystal
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Epidote crystals on a 3mm Pyroxene crystal
09056550014947273584186.jpg
Epidote. 0.6mm tall crystal
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Epidote crystals on a 3mm Pyroxene crystal
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Epidote 0.75mm crystal
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Epidote 0.7mm crystal
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Epidote 0.75mm crystal
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Epidote 0.7mm crystal
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Epidote 0.75mm crystal
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Epidote 0.7mm crystal




Fayalite not found in crystals in this investigation; recorded by Thompson (1969), usually altered to 'Serpentine'.

Furgusonite-Y only found in minute ~0.5mm crystals on a hand full of specimens as single crystals or as small cluster; with a deep clove brown colour, so far not analytically unconfirmed.

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Furgusonite-Y ? 0.5mm crystal


Ferrohornblende rarely found in euhedral vitreous black crystals, with well developed prism faces and terminations measuring to 2mm long, and as swarms of tiny black crystals rarely partly covering K-feldspar crystals.

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Ferrohornblende. 2mm tall crystal
09390340014946660375018.jpg
Ferrohornblende. 1.5mm tall crystal
08816850014946660371382.jpg
Ferrohornblende. 2mm tall crystal
09390340014946660375018.jpg
Ferrohornblende. 1.5mm tall crystal
08816850014946660371382.jpg
Ferrohornblende. 2mm tall crystal
09390340014946660375018.jpg
Ferrohornblende. 1.5mm tall crystal




Ferro-actinolite Forms subheadral crystals with feathery terminations to 1.5mm; the crystals are zoned with ferro-edenite, ferro-richterite, ferro-winchite, katophorite, and riebeckite Tindle (2008)

Fluorapatite has been recorded as a late accessory mineral in the granites, but euhedral crystal in the miarolitic cavities are elusive to say the least. Only one probable crystal was recovered from the unnamed granite, as a double terminated white barrel shaped crystal measuring 1.5mm (assuming that the crystal found is apatite).
04884090014947273592301.jpg
Fluorapatite 1.5mm crystal


Fluorite from the Isle of Skye granites has been found in some unusual crystal variations as well the simple cube and octahedral forms. Of particular interest are well developed colourless-white octahedral crystals pleasingly suspended on hair-like threads of light green hedenbergite, making fine micros. Other isometric habits such as the cube or cubo-octahedron are rare; one specimen was was found with development of dodecahedral faces. The really bizarre fluorite crystals were discovered in the Loch Ainort granite. The fluorite appears to be mostly octahedral crystals elongated along the isometric 'C' axis forming rod-like crystals measuring to 2mm. Interestingly some crystals were found showing a slight twist along the elongation, or even returning back on them selves hook-like.

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Fluorite 1mm crystal
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Fluorite 0.75mm crystal
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Fluorite 1mm crystal
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Fluorite 0.75mm crystal
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Fluorite 1mm crystal
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Fluorite 0.75mm crystal
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Fluorite 1.25mm crystal
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Fluorite 1.5mm crystal
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Fluorite 1.25mm crystal
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Fluorite 1.5mm crystal
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Fluorite 1.25mm crystal
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Fluorite 1.5mm crystal
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Fluorite 0.5mm crystal
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Fluorite 0.6mm crystal
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Fluorite 0.5mm crystal
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Fluorite 0.6mm crystal
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Fluorite 0.5mm crystal
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Fluorite 0.6mm crystal
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Fluorite 1.5mm crystal
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Fluorite 0.7mm crystal
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Fluorite 1.5mm crystal
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Fluorite 0.7mm crystal
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Fluorite 1.5mm crystal
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Fluorite 0.7mm crystal




Gadolinite-Y a rare species from the granites, only so far found in the Loch Ainort granite. All the crystals of gadolinite-Y show some alteration and etching, sometimes with later crystals of allenite-Ce grown on them. The gadolinite-Y crystals are bladed to 1.5mm long, occasionally in sub-parallel groups with a grey green to slighly translucent yellow colour.

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Gadolinite-Y 1mm crystal
05377510014947273623018.jpg
Gadolinite-Y 0.75mm crystal
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Gadolinite-Y 1mm crystal
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Gadolinite-Y 0.75mm crystal
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Gadolinite-Y 1mm crystal
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Gadolinite-Y 0.75mm crystal




Hedenbergite is by far the most common pyroxene species from the Red Hill granites; a small number of granites on the eastern side of the Sligahan river are believed to be riebeckite dominated, but these have not yet been investigated. The hedenberite is found in two crystal habits the more abundant forming a nest of inter-grown acicular hair-like crystals with a light grey-green colour, and has been noted completely filling miarolitic cavities to 2cm. The second crystal variety of hedenbergite is commonly seen as well formed terminated prismatic to near tabular crystals measuring <2mm long, also as sputnik-like groups suspended on hairs of the first type of hedenbergite. The colour of the second habit can be from a lustrous glassy light grey-green to tinted brown.

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Hedenbergite 0.7mm crystals
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Hedenbergite 3cm wide
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Hedenbergite 0.7mm crystals
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Hedenbergite 3cm wide
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Hedenbergite 0.7mm crystals
08048110014947273626138.jpg
Hedenbergite 3cm wide
00201150014947273636711.jpg
Hedenbergite 2mm wide
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Hedenberite 0.75mm crystal
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Hedenbergite 2mm wide
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Hedenberite 0.75mm crystal
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Hedenbergite 2mm wide
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Hedenberite 0.75mm crystal




Heulandite-Ca only rarely found in the Loch Ainort granite as late stage mineral as tiny colourless crystals to 0.2mm. Much more abundant in the Glas Bheinn Mhor granite as crystals to 3mm., not yet noted from the other Red Hill granites. From the Glas Bheinn Mhor granite the heulandite-Ca crystals are distinctively coffin shaped colourless with some development of the {111} faces on the central edges of the crystals.

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Heulandite-Ca 2mm crystal
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Heulandite-Ca 0.6mm crystal with Hedenbergite
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Heulandite-Ca 2mm crystal
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Heulandite-Ca 0.6mm crystal with Hedenbergite
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Heulandite-Ca 2mm crystal
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Heulandite-Ca 0.6mm crystal with Hedenbergite




Ilmenite very rare in euhedral black crystals <0.5mm could be mistaken for distorted Magnetite crystals.

Kainosite-Y is comparatively common in the Loch Ainort granite; the only other granite kainosite-Y has been noted from is the Beinn na Caillich at Corrie Gorm. Kainosite-Y from the Loch Ainort granite occurs in two crystal variants; the most abundant is as blocky to near tabular translucent white crystals measuring to 1mm, which is also the habit that has been found in the Beinn na Caillich granite. The second far less common crystal habit is seen as colourless well formed glassy bladed crystals measuring to 1.5mm long. Kainosite-Y appears to be the last 'granite mineral' to have formed after the titanite on calcite phase, and before the formation of the zeolite and related species.

00071310014946290121340.jpg
Kainosite-Y 0.7mm crystal
08017910014946290111887.jpg
Kainosite-Y 0.6mm crystal with Hedenbergite and Allanite-Ce
00071310014946290121340.jpg
Kainosite-Y 0.7mm crystal
08017910014946290111887.jpg
Kainosite-Y 0.6mm crystal with Hedenbergite and Allanite-Ce
00071310014946290121340.jpg
Kainosite-Y 0.7mm crystal
08017910014946290111887.jpg
Kainosite-Y 0.6mm crystal with Hedenbergite and Allanite-Ce






K and Na-Feldspar as would be expected the mineral is a major constituent of the granite's with quartz.
The feldspars orthoclase and anothite form fine euheadral crystal lineing the miarolitic cavieties, as twinned and untwinned crystals to 0.8cm
04297740014947273639458.jpg
K-Feldspar 5cm wide


Magnetite/Titaniferous Magnetite very common constituent of the all the Isle of Skye granites, but seldom found as euhedral crystals from most of the granites, crystals are all ways small measuring to 0.75mm and octahedral in habit. Magnetite appears to be by far the most abundant from the Beinn na Caillich granite, cavities are commonly scattered with several octahedral crystals to 1mm.

08773020014947203889450.jpg
Magnetite 0.6mm crystal



Marcasite only found as a single partly formed cyclic striated twin measuring 0.2mm,associated with clinochlore and pyrite from the Loch Ainort granite.

Monazite not seen in crystals in this investigation, recoded in thin section by Tindle (2008).

Phlogopite recorded from the so called Marscoite hybrid granite.

Prehnite a late stage mineral formed from the last vestiges of the hydrothermal solutions from the granites along with stilbite-Ca and the other zeolite species. Of this later formed group of minerals the Prehnite is the first, were it develops as tiny thin platy colourless <0.1mm; and as grey translucent cocks-comb like crystal groups measuring to 3mm.

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Prehnite 2mm group
07082490014947273632663.jpg
Prehnite 1mm diameter
05614100014947273635056.jpg
Prehnite 2mm group
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Prehnite 1mm diameter
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Prehnite 2mm group
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Prehnite 1mm diameter




Pyrite very rare as part of a restricted sulphide mineral phase along with sphalerite. The Pyrite is seen as inter-grown groups to 2mm of simple cubic crystals, and may also be associated with late pulse of drusy Quartz on some specimens.

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Pyrite 1.2mm group


Quartz as would be expected quartz is a major constitute of the granites inter-grown with K-feldspar and biotite sometimes displaying areas of 'graphic granite' with the K-feldspar to 1cm. Commonly as sharply formed glassy prismatic crystals to 1cm, rarely seen as lightly smoky crystals to a similar size.

08063640014947273639833.jpg
Quartz 2mm crystal
09698730014947273632147.jpg
Quartz 2mm crystal
08063640014947273639833.jpg
Quartz 2mm crystal
09698730014947273632147.jpg
Quartz 2mm crystal
08063640014947273639833.jpg
Quartz 2mm crystal
09698730014947273632147.jpg
Quartz 2mm crystal
07613100014977542826673.jpg
Smoky Quartz 4mm group




Riebeckite recorded from the Red Hill granite intrusions, but more common in the older granites east of the Sligachan River. It is to be noted that many occurrences of riebeckite from the granite in this study are a zoned mixture of ferro-pyroxenes including ferro-actinolite, ferro-edenite, ferro-richterite, and katophorite (2008) Tindle.

Sphalerite only found rarely as a single crystal in few miarolitic cavities from the Loch Ainort Granite, forming part of very small sulphide phase along with Pyrite, and very rare Marcasite. The Sphalerite crystals measuring to no more than 1.5mm show charicaturistic triangular growth pattens; and are invariably thinly coated by light brown 'Limonite', or altered Clinochore. The Spalerite crystals contain a small percentage of Copper (M.Rothwell priv com).

02134180014947273641027.jpg
Sphalerite 1.5mm crystal
03408620014947273649202.jpg
Sphalerite 1mm crystal
02134180014947273641027.jpg
Sphalerite 1.5mm crystal
03408620014947273649202.jpg
Sphalerite 1mm crystal
02134180014947273641027.jpg
Sphalerite 1.5mm crystal
03408620014947273649202.jpg
Sphalerite 1mm crystal




Stilbite-Ca a common late stage zeolite forming fine colourless crystals in radial groups of thickend bladed habit measuring to 4mm, with some development of the {110} and {111} faces. Stilbite-Ca also forms in crystals to 0.7mm with the prism faces terminated by flat {111} face. A recent analysis (M.Rumsey priv com) has shown that some of the Stilbite from the Beinn an Dubhaich Granite has a percentage of potassium with in the structure may be corresponding to (Ca,K,Na)4[Al9Si27O72]·nH2O postulated by the author.

00838790014947244386196.jpg
Stilbite-Ca 0.75mm spray
06813840014947244385349.jpg
Stilbite-Ca 1.5mm crystal group
00838790014947244386196.jpg
Stilbite-Ca 0.75mm spray
06813840014947244385349.jpg
Stilbite-Ca 1.5mm crystal group
00838790014947244386196.jpg
Stilbite-Ca 0.75mm spray
06813840014947244385349.jpg
Stilbite-Ca 1.5mm crystal group
06067700014947244382997.jpg
Stilbite-Ca 1.5mm crystal group with Heulandite



Sulphur very rare found as tiny pale yellow spheralites to 0.1mm near to slightly etched crystals of sphalerite.

Synchysite-Y note as a single possible reddish prismatic barrel-like crystal to 0.2mm which might be this species.

06909610014947273642434.jpg
Synchysite ? 0.2mm crystal


Titanite common in the granites investigated in this study. The titanite crystals have four noted crystal habits; abundant as usually white to beige tiny crystals to 0.5mm with simple crystal habit. This crystal habit of Titanite is a late phase forming after calcite, and rarely forming epimorphs after calcite crystals. Another less common crystal habit of titanite is seen as broad wedge shaped crystals measuring to 1.5mm with a translucent white to tinted pink colour. Not uncommon as discreet curving crystal groups measuring to 1mm of tiny white crystals stacked on top of one an other in a segmented habit. A small number of single sparsely scattered prismatic crystals to 1.5mm long were found from the unnamed granite.

07978620014946288728467.jpg
Titanite 1mm crystal
00418520014947273655497.jpg
Titanite 0.6mm crystal
07978620014946288728467.jpg
Titanite 1mm crystal
00418520014947273655497.jpg
Titanite 0.6mm crystal
07978620014946288728467.jpg
Titanite 1mm crystal
00418520014947273655497.jpg
Titanite 0.6mm crystal



Zircon probably the micro-mineral prize from the Loch Ainort granite to be noted for the gemmy prismatic crystals measuring to 2.5mm long, with a fine orange to yellow colour, rarely light opaque beige. Zircon is also quite abundant in crystals to 1mm on edge only with development of the pyramid faces. The colour in this later habit is more varied from light beige, and light lemon yellow to orange. Rare deep brick red crystals to 0.3mm have been found in the Beinn an Dubhaich granite, rarely from the unnamed granite as light beige crystals.

01543890014947273658426.jpg
Zircon 2mm crystal
02293030014947273654732.jpg
Zircon 1mm crystal
01543890014947273658426.jpg
Zircon 2mm crystal
02293030014947273654732.jpg
Zircon 1mm crystal
01543890014947273658426.jpg
Zircon 2mm crystal
02293030014947273654732.jpg
Zircon 1mm crystal
03486110014947273656599.jpg
Zircon 0.7mm crystal
03771810014947273652121.jpg
Zircon 0.6mm crystal
03486110014947273656599.jpg
Zircon 0.7mm crystal
03771810014947273652121.jpg
Zircon 0.6mm crystal
03486110014947273656599.jpg
Zircon 0.7mm crystal
03771810014947273652121.jpg
Zircon 0.6mm crystal
04151770014947273653633.jpg
Zircon 1.5mm crystal
05773080014947273653071.jpg
Zircon 0.7mm crystal
04151770014947273653633.jpg
Zircon 1.5mm crystal
05773080014947273653071.jpg
Zircon 0.7mm crystal
04151770014947273653633.jpg
Zircon 1.5mm crystal
05773080014947273653071.jpg
Zircon 0.7mm crystal




Note: Some of the Landscape Photographs are Copyright © geograph.org.uk - Creative Commons Attribution Licence - Some Rights Reserved Wikicommons

There appear to be no current restrictions on collecting from the area please follow the collecting code.

Acknowledgements
Thanks are due to Mike Rumsey, Andy Tindle, David Green the late Mike Rothwell.
And to Christine Rust for her helpful advice.

Refs:-

Bell, B. R. & Harris, J. W. (1986). An Excursion Guide to the Geology of the
Isle of Skye. Geological Society of Glasgow, 317 pp.

Bell, B. R., Claydon, R. V. & Rogers, G. (1994). The petrology and geochemistry of cone-sheets from the Cuillin Igneous Complex,
Isle of Skye: evidence for combined assimilation and fractional crystallization during lithospheric extension.
Journal of Petrology 35, 1055–1094.

Bell, J.D., (1976) The Tertiary intrusive complex on the Isle of Skye, Proceedings of the Geologists' Association, 87, 247-271.

Exley, R.A. (1980) Microprobe studies of REE-rich accessory minerals: Implications for Skye granite petrogenesis
and REE mobility in hydrothermal systems. Earth and Planetary Science Letters, 48, 97-l10

Harker, A. (1904) The Tertiary Igneous Rocks of Skye. Mem. geol. Surv. U.K.H.M.S.O. Edinburgh

Tilley, C. E. (1951) The zoned contact-skarns of the Broadford area, Skye: a study of boron-fluorine metasomatism
in dolomites. Min Mag 29. 621-666.

Tindle, A. G. (2008) Minerals of Britain and Ireland, Terra Publishing.

Thompson, R. N. (1969) Tertiary granites and associated rocks of the Marsco area, Isle of Skye. Quarterly Journal of the Geological Soceity London. 124, 349-385.

Wager, L. R., D. S. Weedoz,D. S., and Vincent, E. A. (1953)
A granophyre from Coire Uaigneich, Isle of Skye, containing quartz paramorphs after tridymite. Min Mag 30. 263-276.

07380250014947273658237.jpg
Zircon 0.5mm crystal




Article has been viewed at least 9924 times.

Discuss this Article

14th Apr 2013 14:33 BSTMichael Wood

Nice article Steve; well explained and good photographs. Thank you for your effort!
Mike Wood

15th Apr 2013 00:15 BSTChester S. Lemanski, Jr. Manager

Steve,

This article is a work of art! Thank you so much for taking the time to prepare it and share it with the Mindat community!!

Chet Lemanski

15th Apr 2013 09:07 BSTRui Nunes Expert

Steve,
Great article and nice photos! Thank you for sharing...
Rui Nunes

16th Apr 2013 09:37 BSTMalcolm Southwood Expert

Steve,
I really enjoyed this article - and great photos!
mal

16th Apr 2013 18:34 BSTHarjo Neutkens Manager

Great article Steve!

17th Apr 2013 02:39 BSTSteven Kuitems Expert

What a delightful article Steve!! It sounds like a micro-mounters paradise. I can certainly see the need for a good sledge hammer workout at the site. Great photos!!

18th Apr 2013 17:55 BST

Steve,
Very interesting and well illustrated article. Seems like a great area for collecting micros.

18th Apr 2013 18:52 BSTKnut Eldjarn Manager

Excellent article and fabulous photos. I have been aware of the Ca-silicate assemblages and zeolites from the Isle of Sky and a description of the mineralogy of the granite intrusions makes a very interesting addition to the mineralogy of this famous area. Thanks for sharing.
Knut

9th May 2013 17:58 BSTDave Crosby

Ditto! Well researched and presented!

24th Oct 2013 19:15 BSTStephen Burchmore (2)

Good work Steve, great photos, I think I will have another look through some of my Granite's

24th Dec 2015 04:30 GMTD Mike Reinke

Steve,
Thanks for this article. I recently started scrounging up vuggy, pock marked red granites from the shore of Lake Michigan, Zion, Illinois, USA. I haven't found the diversity of minerals you have, of course, but you helped me ID apophyllite, at least tentatively. Thanks. Nice photos too.
 
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