Sanidine
Current inventory: 0 gems
 

  
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)

Chemistry

Chemical Formula:

(K,Na)(Al,Si)₄O₈

Potassium Sodium Aluminum Silicate

Molecular Weight:

274.30 gm

Composition:

Potassium

10.69 %

K

12.88 %

K₂O

Sodium

2.10 %

Na

2.82 %

Na₂O

Aluminum

9.84 %

Al

18.59 %

Al₂O₃

Silicon

30.72 %

Si

65.71 %

SiO₂

Oxygen

46.66 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/J.06-20

Nickel-Strunz 10th Ed. ID:

9.FA.30

9 : SILICATES (Germanates)
F : Tektosilicates without zeolitic H₂O
A : Tektosilicates without additional non-tetrahedral anions

Related to:

Feldspar Group. Sanidine-Albite Series. Potassium Feldspars (K-Feldspars).

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 

Varieties:

Azulicite, Barium-Sanidine, Citron Feldspar

Synonyms:

Glassy Feldspar, Gränzerite, K-spar, potassium Feldspar, Rhyacolite, Riacolite

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals commonly tabular on {010}, with a square cross section, to 50 cm. Acicular in spherulites.

Twinning:

Carlsbad twins are common, Baveno and Manebach twins rarer

Physical Properties

Cleavage:

Perfect on {001}, distinct on {010}; parting on {100}

Fracture:

Irregular/uneven, Conchoidal

Tenacity:

Brittle

Moh's Hardness:

6.0

Density:

2.56 - 2.62 (g/cm³)

Luminescence:

None

Radioactivity:

Barely Detectable; GRapi = 152.94 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Colorless, white, gray, yellowish white, reddish white, very rarely blue (Azulicite); colorless in thin section

Transparency:

Transparent to translucent

Luster:

Vitreous, pearly on cleavages

Refractive Index:

1.518 - 1.531  Biaxial ( - )

Birefringence:

0.006 - 0.007

Dispersion:

Weak; r < v or r > v

Pleochroism:

None

Occurances

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.

Common Associations:

Quartz, sodic Plagioclase, Muscovite, Biotite, hornblende, Magnetite

Common Impurities:

Fe, Ca, Na, H₂O

Type Locality:

Drachenfels, Königswinter, Siebengebirge, North Rhine-Westphalia, Germany

Year Discovered:

1808

View mineral photos:

Sanidine Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

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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