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| Sanidine
was named in 1808 by Karl Wilhelm Nose (1753-1835)
from the Greek words
σάνις (sanis)
meaning a tablet and ιδος
(idos) meaning to appear in allusion to the mineral's common flattened tabular
crystal habit.
| Discovered
in 1808; IMA
status:
Valid (pre-IMA; Grandfathered) |
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Chemistry
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Chemical
Formula: |
(K,Na)(Al,Si)4O8
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Potassium
Sodium Aluminum Silicate |
Molecular
Weight: |
274.30 gm
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Composition: |
Potassium |
10.69 % |
K |
12.88 % |
K2O |
|
Sodium |
2.10 % |
Na |
2.82 % |
Na2O |
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Aluminum |
9.84 % |
Al |
18.59 % |
Al2O3 |
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Silicon |
30.72 % |
Si |
65.71 % |
SiO2 |
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Oxygen |
46.66 % |
O |
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100.00 % |
|
100.00 % |
= TOTAL OXIDE |
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Classification
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Mineral
Classification: |
Silicates
(Germanates)
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Strunz 8th
Ed. ID:
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8/J.06-20
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Nickel-Strunz 10th
Ed. ID:
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9.FA.30
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9 : SILICATES (Germanates)
F : Tektosilicates without zeolitic H2O
A : Tektosilicates without additional non-tetrahedral anions
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Related
to: |
Feldspar
Group.
Sanidine-Albite
Series. Potassium Feldspars (K-Feldspars).
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Members
of Group: |
Feldspar
Group:
Albite,
Amazonite, Andesine, Anorthite, Anorthoclase, Banalsite,
Buddingtonite, Bytownite, Celsian, Dmisteinbergite,
Hyalophane, Labradorite, Microcline, Oligoclase, Orthoclase,
Paracelsian, Reedmergnerite, Sanidine, Slawsonite, Stronalsite,
Svyatoslavite
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Varieties: |
Azulicite,
Barium-Sanidine, Citron Feldspar
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Synonyms: |
Glassy Feldspar,
Gränzerite, K-spar, potassium Feldspar, Rhyacolite,
Riacolite
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Crystal
Data
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Crystallography:
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Monoclinic - Prismatic
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Crystal
Habit:
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Crystals
commonly tabular on {010}, with a square cross section,
to 50 cm. Acicular in spherulites.
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Twinning:
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Carlsbad
twins are common, Baveno and Manebach twins rarer
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Physical
Properties
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Cleavage: |
Perfect
on {001}, distinct on {010}; parting on {100}
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Fracture: |
Irregular/uneven,
Conchoidal
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Tenacity:
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Brittle
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Moh's
Hardness: |
6.0
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Density:
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2.56
- 2.62 (g/cm3)
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Luminescence:
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None
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Radioactivity:
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Barely
Detectable;
GRapi = 152.94 (Gamma Ray American Petroleum Institute Units)
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Optical
Properties
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Color: |
Colorless,
white, gray, yellowish white, reddish white, very rarely
blue (Azulicite); colorless in thin section
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Transparency: |
Transparent
to translucent |
Luster: |
Vitreous,
pearly on cleavages |
Refractive
Index: |
1.518
- 1.531 Biaxial ( - )
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Birefringence: |
0.006
- 0.007
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Dispersion: |
Weak; r
< v or r > v |
Pleochroism: |
None |
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Occurances
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Geological
Setting: |
Most
common in felsic volcanic and hypabyssal rocks as rhyolites,
phonolites, trachytes; as spherulites in volcanic glass.
Also from ultrapotassic mafic, high-temperature contact
metamorphic (sanidinite facies), and hydrothermally
altered rocks. From eclogite nodules in kimberlite.
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Common
Associations: |
Quartz,
sodic Plagioclase, Muscovite, Biotite, hornblende, Magnetite
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Common
Impurities: |
Fe,
Ca, Na, H2O
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Type
Locality: |
Drachenfels, Königswinter, Siebengebirge, North Rhine-Westphalia, Germany
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Year
Discovered: |
1808
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View
mineral photos: |
Sanidine
Mineral Photos and Locations |
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More
Information
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Mindat.org
Webmineral.com
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Sanidine
is a member of the alkali,
or potassium Feldspars (K-Feldspars) of the Feldspar Group of minerals that includes Albite,
Amazonite,
Andesine, Anorthite, Bytownite, Hyalophane, Labradorite,
Moonstone,
Oligoclase, Orthoclase, Sanidine
and Sunstone. The
K-Feldspars include Anorthoclase, Microcline, Orthoclase
and Sanidine. Sanidine forms a series with Albite with
Sanidine being the potassium (K) rich end member and
Albite being the sodium (Na) rich end member and Anorthoclase
being an intermediate member with about 10 to 36% sodium
content. Sanidine is typically found in felsic volcanic rocks such as obsidian, rhyolite and trachyte.
Sanidine
was named in 1808 by Karl Wilhelm Nose (1753-1835)
from the Greek words
σάνις (sanis)
meaning tablet and ιδος
(idos) meaning to appear in allusion to the mineral's common flattened, tabular
crystal habit. Sanidine was described by Nose as glassy
tabular crystals from volcanic rocks of the lower Rhine
Valley, Germany.
Sanidine is a fairly
rare mineral and even rarer as a faceted
gem as crystals are rarely large enough for faceting. It is
found in several locations around the world but the
main source of Sanidine gems is Itrongay, Mahasoa East Commune, Betroka District, Anosy Region, Tuléar Province, Madagascar.
Large, gem quality crystals from this location have
been found in bright yellow to straw yellow and greenish-yellow
crystals up to about 100 carats from as early as the
early 1900's. Until recently these crystals (and gems)
were incorrectly labeled as "Orthoclase" instead
of Sanidine. Sanidine gems from Madagascar are exceptional
in their size, clarity, saturation and uniformity of
color.
Sanidine
distribution: Not uncommon, but rare in crystals of
any size. In Germany, from Drachenfels, Siebengebirge,
Rhine; and at Hohenfels, Mendig, Mayen, and elsewhere
around the Laacher See, Eifel district. In France, at
Mt. Dore, Auvergne, and Puy Gros du Laney, Puy-de-Dôme.
From Vesuvius and Monte Somma, Campania, and Monte Cimine,
Lazio, Italy. At Daichi, Wakayama Prefecture, Japan.
From Kanchin-do, Meisem-gun, northeast Korea. In the
USA, at Tooele, Tooele County, Utah; Cottonwood Canyon,
Peloncillo Mountains, Cochise County, Arizona; as large
crystals in Rabb Canyon and near the crest of the Black
Range, Grant County, New Mexico. From Bernic Lake, Manitoba,
and Mont Saint-Hilaire, Quebec, Canada. In Mexico at
the (early 1990's) Pili Mine, Mun. de Saucillo, Chihuahua, and
at Sierra de San Francisco, Durango. At Itrongay, Mahasoa East Commune, Betroka District, Anosy Region, Tuléar Province, Madagascar.
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