The Mineral MICROCLINE
- Chemistry: KAlSi3 O8 , Potassium aluminum silicate.
- Class: Silicates
- Subclass: Tectosilicates
- Group: Feldspars
- Uses: ornamental stone, in the manufacture of glass, enamel and porcelain products and as mineral specimens.
Specimens
Microcline is a common, but not a well known mineral and has been used as a semi-precious stone under the names of Amazonite and Perthite. Amazonite is a variety that is deep green and is suitable for carving and polishing. The perthite variety is a stripped, veined or almost zebra patterened stone, that is produced from lamellar intergrowths inside the crystal. These intergrowths result from compatible chemistries at high temperatures becoming incompatible at lower temperatures and thus a seperating and layering of these two phases. The colored stripes are microcline and the white or clear stripes are plagioclase feldspars. If there is more plagioclase than microcline it is called "antiperthite".
Microcline is a polymorph of other minerals that share the same chemistry but have different crystal structures.
If positive identification can not be made by field methods then the specimen may be refered to as a potassium feldspar or K-spar.
The other k-spar minerals are sanidine,
orthoclase and
Twinning is common in all feldspars and follow certain twin laws such as the Albite Law, the Pericline Law, the Carlsbad Law, the Manebach Law and the Baveno Law. Albite and pericline Law type twinning produce stacks of twin layers that are typically only fractions of millimeters to several millimeters thick. These twinned layers can be seen as striation like grooves on the surface of the crystal and unlike true striations these also appear on the cleavage surfaces. Albite and pericline twinning is more common in plagioclase feldspars than with microcline. The Carlsbad Law twin produces what appears to be two intergrown crystals growing in opposite directions. Two different twin laws, the Manebach and Baveno laws, produce crystals with one prominant mirror plane and penetrant angles or notches into the crystal. Single crystals showing a perfect twin are rare and are often collected by twin fanciers.
Well formed crystals can be quite striking in appearance. At some localities fine amazonite clusters are intermixed with smoky quartz crystals and this results in an outstanding classic mineral specimen.
PHYSICAL CHARACTERISTICS:
- Color is usually off-white,yellowish, flesh pink, brown or green.
- Luster is vitreous to sometimes pearly or dull if weathered.
- Transparency crystals are translucent, but usually translucent to opaque.
- Crystal System is triclinic; bar 1
- Crystal Habits include blocky, or tabular crystals. Crystals have a nearly rectangular or square cross-section with slightly slanted dome and pinacoid terminations. Twinning is common. Crystals can be twinned according to the Albite, Pericline, Carlsbad, Manebach and Baveno laws. Microcline can be found as a major rock forming component in granites, syenites and in metamorphic gneisses.
- Cleavage is perfect in one and good in another direction forming nearly right angled prisms.
- Fracture is conchoidal.
- Hardness is 6 - 6.5.
- Specific Gravity is approximately 2.5 (average)
- Streak is white.
- Associated Minerals are quartz, muscovite and plagioclase feldspars.
- Other Characteristics: Lamellar twinning may cause a grooved effect on cystal and cleavage surfaces that appear as striations. Perthite intergrowths causes a stripped appearance is some specimens.
- Notable Occurrences include Pikes Peak region of Colorado and North Carolina among other sites in the USA; Russia; Norway and Madagascar.
- Best Field Indicators are occurence, twinning, color and luster.
 Amethyst Galleries' Mineral Gallery MINERALS |
MICROCLINE specimen mic-1
$ 50.00
$ 50.00
Dims: 1-5/8" x 1-1/2" x 1-1/8"
Wt: 1.86 oz
Two Point Mine, Florissant, Teller Co., Colorado, U.S.A.
Though incomplete, this Microcline specimen is quite beautiful. It is of the variety Amazonite, the blue-green Microcline that is sometimes cut as a gemstone. The specimen consists of two crystals that form a penetration twin. The break that separated the specimen from its place of formation is angled so that at least 3 sides are incomplete, and a small part of each crystal's basal pinacoid termination is missing. The crystal and termination faces that still exist are clean and free of damage. The color is a uniform, deep blue-green.
mic-1 ($ 50.00)
Two Point Mine, Florissant, Teller Co., Colorado, U.S.A.
MICROCLINE specimen mic-2
$ 70.00
$ 70.00
Dims: 2-1/2" x 2-1/8" x 1-3/8"
Wt: 3.27 oz
Crystal Peak Mining Dist., Lake George, Park Co., Colorado, U.S.A.
This specimen is made up of two complete crystals of Microcline that are growing out of a larger, incomplete crystal. The incomplete crystal measures 1-1/8 x 1-1/2 in width and depth(its length is severely curtailed due to breakage). Both of the other crystals have collective dimensions of 1-1/2" x 1-1/8" x 3/4"; they are completely free of damage, and almost identical in structure, probably due to the fact that together they form a Carlsbad Twin. Their color is the obligatory beige of most orthoclase crystals.
mic-2 ($ 70.00)
Crystal Peak Mining Dist., Lake George, Park Co., Colorado, U.S.A.
MICROCLINE specimen mic-3
$ 36.00
$ 36.00
Dims: 2.0" x 2.0" x 1.8" (5.1 x 5.1 x 4.6 cm)
Wt: 3.55 oz. (100.9 g)
Minas Gerais, Brazil
This specimen consists of a cluster of 5 partly intergrown Microcline crystals. These crystals range in size from 0.4 x 0.4 x 0.3" (1.0 x 1.0 x 0.8 cm) to 1.8 x 1.6 x 1.0" (4.6 x 4.1 x 2.0 cm) and show weathered but good triclinic prismatic form. Their edges are straight and mostly well-defined, and their faces are flat. However, there are many small hollows that extend into each crystal. These are definitely of natural origin and geometric in form. The crystals have a pale cream coloration and a dull, matte luster, and are completely opaque. There is no host rock present on the specimen, but several tiny muscovite books are clustered together where two of the crystals meet.
mic-3 ($ 36.00)
Minas Gerais, Brazil
MICROCLINE specimen mic-4
$ 36.00
$ 36.00
Dims: 3.0" x 2.3" x 1.9" (7.6 x 5.8 x 4.8 cm)
Wt: 3.56 oz. (101.1 g)
Minas Gerais, Brazil
This particular specimen reminds me more of albite than Microcline, actually. It consists of a confusing association of dozens of intergrown Microcline crystals. These crystals range in size from 2 x 2 x 2 mm to 1.0 x 0.7 x 0.6" (2.5 x 1.8 x 1.5 cm) and show so many oddities and inconsistencies in growth that it is difficult to tell one crystal from another. All have a creamy color and a dull-to-waxy luster, and are completely opaque. Among the profusion of intergrowth are many small books of muscovite and at least 7 hexagonal prismatic quartz crystals. The muscovites show definite hexgonal outlines and do not exceed 0.4" (1.0 cm) in diameter. The quartz crystals reach a maximum length of 0.8" (2.0 cm) and show excellent hexagonal prismatic form. They are colorless and have a bright, vitreous luster, and are transparent and very clear.
mic-4 ($ 36.00)
Minas Gerais, Brazil
MICROCLINE specimen mic-5
$ 40.00
$ 40.00
Dims: 1.7" x 1.2" x 1.2" (4.3 x 3.0 x 3.0 cm)
Wt: 1.72 oz. (48.8 g)
Crystal Peak Mining District, Lake George, Park County, Colorado, U.S.A.
A single Microcline crystal attached to a small amount of albite makes up this specimen. The Microcline is of the variety known as Amazonite, and shows its characteristic pale bluish-green coloration. The crystal is in excellent condition, showing no human-induced damage, and has excellent triclinic form; even its underside seems to have attempted to form a crystalline face! The Amazonite has a pearly luster and is translucent only along its edges, even in halogen light. The attached albite is heavily damaged and shows almost no discernable form.
mic-5 ($ 40.00)
Crystal Peak Mining District, Lake George, Park County, Colorado, U.S.A.
MICROCLINE specimen mic-6
$ 25.00
$ 25.00
Dims: 1.0 x 1.0 x 0.9" (2.5 x 2.5 x 2.3 cm)
Wt: 14.4 g
10 Percenter Mine, Teller County, Colorado, U.S.A.
This small thumbnail specimen consists of a single, undamaged crystal of the variety of Microcline that is known as Amazonite. It is in near-perfect condition and has excellent triclinic prismatic form, with well-defined edges and clean faces that show a pearly luster. The crystal appears to be doubly-terminated, but one termination is incomplete due to its intergrowth with some albite, most of which has been removed. It has the standard pale aqua-blue coloration that is common for Amazonite and shows dim translucence around its edges. Besides the attached albite, there is no host rock.
mic-6 ($ 25.00)
10 Percenter Mine, Teller County, Colorado, U.S.A.
MICROCLINE specimen mic-7
$ 55.00
$ 55.00
Dims: 2.2 x 1.6 x 1.6" (5.6 x 4.1 x 4.1 cm)
Wt: 4.9 oz. (138.4 g)
Crystal Park, Teller County, Colorado, U.S.A.
This simple hand specimen consists of a single monoclinic prismatic crystal of Amazonite, a blue-green variety of Microcline. It is in excellent condition, showing only a small amount of damage along one edge of its termination. Its form is exceptional- even the breakage at its base, where it broke prior to mining, has been partly healed. Its edges are well-defined and its faces are smooth and clean, possessing a pearly luster. Though showing some discoloration, it basically has a good, moderate bluish-green coloration. Some of its prism faces are a bit more rough in texture than others, and have a characteristically paler color. The clearer ones show the thin, pale lines that make up the standard visual texture of this material. There is no host rock present. This is one of the larger Amazonite crystals that I have seen available.
mic-7 ($ 55.00)
Crystal Park, Teller County, Colorado, U.S.A.
MICROCLINE specimen mic-8
$ 35.00
$ 35.00
Dims: 1.5 x 1.3 x 1.2" (3.8 x 3.3 x 3.0 cm)
Wt: 1.99 oz. (56.5 g)
Sceptre Claims, Emerald Lake, Yukon Territory, Canada
The twinned Microcline crystal that makes up this specimen is incomplete, but the associated damage is old, having occurred prior to mining. Where intact, it has good triclinic prismatic form and shows strong evidence of Mannenbach-Baveno twinning One can easily see the twinning plane on the most complete face. Its edges are relatively well-defined and its faces are often striated but clean and possess a dull pearly luster. The crystal has a pale yellow color that may be due to rust-staining and is translucent, showing small areas of transparence in between the internal cleavage planes and assorted inclusions and internal fractures. A patch of tiny, dark brown crystals are present- I believe that they are calcites with very heavy iron inclusions. There is no host rock, and the piece is hot-glued onto a flat acrylic base.
mic-8 ($ 35.00)
Sceptre Claims, Emerald Lake, Yukon Territory, Canada
MICROCLINE specimen mic-9
$ 32.00
$ 32.00
Dims: 2.0 x 1.8 x 0.9" (5.1 x 4.6 x 2.3 cm)
Wt: 1.40 oz. (39.8 g)
Broken Hill Mine, New South Wales, Australia
This small hand specimen consists of a broken chunck of Microcline, a member of the feldspar group. This piece is in fair to poor condition, showing much breakage, and has crystalline tendencies but no actual crystal form. Some surfaces are flat and apparently cleaved- these have a pearly luster- but others are obviously freshly broken, and have a brighter, vitreous luster. The grass-green color of the material is quite striking, however, as is the fact that it is translucent and contains areas of dim transaprence. There are a few bits of broken, crystalline galena present, and possibly some milky quartz, though it could just be more Microcline with a gray coloration.
mic-9 ($ 32.00)
Broken Hill Mine, New South Wales, Australia
MICROCLINE specimen mic-10
$ 36.00
$ 36.00
Dims: 1.1 x 1.0 x 0.9" (2.8 x 2.5 x 2.3 cm)
Wt: 19.0 g w/ specimen box
Rocket Claim, Teller County, Colorado, U.S.A.
At least 4 Amazonite crystals are intergrown on this specimen. These crystals do not measure more than 0.4" (1.0 cm) along any axis but are in excellent condition, showing very little damage. Their triclinic prismatic form is very good, though there is some slight warping due to intergrowth. All have a pale blue-green coloration and a dull pearly luster. They are accompanied by 3 smoky quartz crystals, only two of which are complete. The piece is glued into a plastic specimen box.
mic-10 ($ 36.00)
Rocket Claim, Teller County, Colorado, U.S.A.
MICROCLINE specimen mic-11
$ 45.00
$ 45.00
Dims: 2.6 x 2.5 x 1.6" (6.7 x 6.4 x 4.1 cm)
Wt: 4.4 oz. (126 g)
Crystal Peak Mining District, Lake George, Park County, Colorado, U.S.A.
This hand specimen consists of a nearly complete Microcline crystal that is accompanied by 3 smoky quartz crystals. The Microcline has dimensions of 1.8 x 1.3 x 1.2" (4.6 x 3.3 x 3.0 cm) and is in excellent condition, showing almost no fresh damage. Its triclinic prismatic form is very good, though slightly warped due to intergrowth, and it has the standard blue-green color and waxy luster. Bits of several other Microcline crystals are present, but none of these are more than 20% complete. The accompanying smoky quartzes are also in excellent condition and have a somewhat flattened hexagonal prismatic form. Their dark brown color is good, their vitreous luster is rather dull, and they are dimly transparent and mostly cloudy.
mic-11 ($ 45.00)
Crystal Peak Mining District, Lake George, Park County, Colorado, U.S.A.
MICROCLINE specimen mic-12
$ 25.00
$ 25.00
Dims: 0.6 x 0.6 x 0.4" (1.6 x 1.6 x 1.0 cm)
Wt: oz. ( g)
Park County, Colorado, U.S.A.
Part of a single, twinned Microcline crystal makes up this small thumbnail specimen. Though it is broken and incomplete, the breakage occurred prior to mining and is slightly healed over. It shows excellent triclinic form, and the twinning, in accordance with the Carlsbad-Law, is excellent and easily visible. It has a creamy, pale brown color and a waxy luster. The crystal is free of any host material and is affixed inside a plastic specimen box with a removable putty.
mic-12 ($ 25.00)
Park County, Colorado, U.S.A.
MICROCLINE specimen mic-13
$ 45.00
$ 45.00
Dims: 1.5 x 1.4 x 1.2" (3.9 x 3.5 x 3.0 cm)
Wt: 1.0 oz. (28 g)
Crystal Creek, Florissant, Teller County, Colorado, U.S.A.
This hand specimen consists of a single Amazonite (green Microcline) prism that extends from a Perthite ("striped" Microcline) base. This crystal is in good condition, though it looks as if it may have been broken and repaired. If it is repaired, then the repair job is extremely good, as only a heavy crack is evident. The crystal measures 1.3 x 0.9 x 0.5" (3.3 x 2.2 x 1.2 cm) and has a somewhat warped triclinic form that has an odd trait- portions of the green Amazonite crystal seem to fade into the Perthite base with no solid boundary, so that the green color slowly fades and the crystal form slowly becomes massive. Its blue-green color and pearly luster are standard for the specie. A few small, dark smoky quartzes extend sideways from the base of the crystal- one is damaged, but all have excellent form, color and clarity.
mic-13 ($ 45.00)
Crystal Creek, Florissant, Teller County, Colorado, U.S.A.
MICROCLINE specimen mic-14
$ 55.00
$ 55.00
Dims: 1.2 x 1.1 x 1.1" (3.0 x 2.8 x 2.7 cm)
Wt: 20 g
Crystal Creek, Florissant, Teller County, Colorado, U.S.A.
Three Amazonite (green Microcline) crystals make up the bulk of this small hand specimen- however, only one of these is complete or undamaged. This crystal is also the largest, and has dimensions of 0.9 x 0.7 x 0.6" (2.2 x 1.9 x 1.5 cm). Its triclinic prismatic form is excellent and its green-blue color and pearly luster are standard for its specie. A few stubby smoky quartz crystals are present, and all seem to extend from a small orthoclase base.
mic-14 ($ 55.00)
Crystal Creek, Florissant, Teller County, Colorado, U.S.A.
MICROCLINE specimen mic-15
$ 35.00
$ 35.00
Dims: 2.2 x 2.1 x 1.9" (5.5 x 5.3 x 4.9 cm)
Wt: 2.9 oz. (81 g)
Mount Saint Hilaire, Quebec, Canada
At least 4 intersecting Microcline crystals make up the bulk of this large hand specimen. These crystals are generally worn and incomplete, but all damage appears to have occurred prior to mining. The largest (and seemingly most complete) of the crystals has dimensions of 1.8 x 1.4 x 0.5" (4.5 x 3.5 x 1.3 cm) and a nearly tabular triclinic form that is not very well defined. All have a dull white coloration and a waxy luster at best. They are accompanied by two muscovite books that have an almost rosette form, a cluster of albite blades and what looks like a formation of dark brown, dull "angel-wing" calcite- however, I am not sure exactly what the mineral is.
mic-15 ($ 35.00)
Mount Saint Hilaire, Quebec, Canada
MICROCLINE specimen mic-16
$ 150.00
$ 150.00
Dims: 2.1 x 1.9 x 1.7" (5.4 x 4.7 x 4.2 cm)
Wt: 3.4 oz. (97 g)
Bob and Ray Pocket, Crystal Creek, Florissant, Teller County, Colorado, U.S.A.
This hand specimen consists of a single large Microcline crystal that is in very good condition; it shows light damage at its termination but is otherwise intact. Its monoclinic prismatic form is likewise very good, showing obvious twinning. A few zones of white plagioclase are present in the crystal, earning this specimen the name "Perthite". Otherwise, the crystal has the standard blue-green coloration and a pearly-to-waxy luster. It extends from a base made up of albite and another, fractured and incomplete Amazonite.
mic-16 ($150.00)
Bob and Ray Pocket, Crystal Creek, Florissant, Teller County, Colorado, U.S.A.