ClassicGems.net

Andesine (variety of Albite, Feldspar)

Discovered in 1841;   IMA status: Not Valid (a variety of Albite, Feldspar)

Chemistry

Chemical Formula:

(Na,Ca)[Al(Si,Al)Si₂O₈]

Sodium Calcium Aluminum Silicate

Molecular Weight:

521.21 gm

Composition:

Sodium

5.14 %

Na

6.92 %

Na₂O

Calcium

5.97 %

Ca

8.35 %

CaO

Aluminum

14.06 %

Al

26.57 %

Al₂O₃

Silicon

27.18 %

Si

58.16 %

SiO₂

Oxygen

47.65 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/J.07-40

Nickel-Strunz 10th Ed. ID:

9.FA.35

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

Related to:

Feldspar Group. Plagioclase Series. Low- and high-temperature structural modifications are recognized.

Members of Group:

Feldspar Group: Albite, Andesine, Anorthoclase, Banalsite, Buddingtonite, Bytownite, Celsian, Dmisteinbergite, Hyalophane, Labradorite, Microline, Oligoclase, Orthoclase, Paracelsian, Reedmergnerite, Sanidine, Slawsonite, Stronalsite, Svyatoslavite

Varieties:

None

Synonyms:

Andesite (of Dana)

Crystal Data

Crystallography:

Triclinic - Pinacoidal

Crystal Habit:

Crystals rare, to 2 cm; commonly massive, cleavable, or granular.

Twinning:

Commonly twinned after Albite, Pericline, and Carlsbad laws. Also twinned after a law similar to the Manebach law.

Physical Properties

Cleavage:

Perfect on {001}, less Perfect on {010}, {110} observed

Fracture:

Irregular/Uneven to Conchoidal

Tenacity:

Brittle

Moh's Hardness:

6.0 - 6.5

Density:

2.66 - 2.68 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

White, Grayish, Green, Yellow, Reddish, Orangish-Red, Red

Transparency:

Transparent to Translucent

Luster:

Subvitreous to Pearly

Refractive Index:

1.543 - 1.562  Biaxial ( +/- )

Birefringence:

0.0080 - 0.0090

Dispersion:

Weak, r > v

Pleochroism:

None

Occurances

Geological Setting:

Widespread in igneous rocks of intermediate silica content, as syenites and andesites. Characteristic of granulite to amphibolite facies metamorphism, commonly as antiperthite; as detrital grains in sedimentary rocks.

Common Associations:

Quartz, Potassic Feldspar, Biotite, Hornblende, Magnetite

Common Impurities:

None

Type Locality:

Marmato Mine, Marmato, Cauca, Chocó Department, Colombia

Year Discovered:

1841

View mineral photos:

Andesine Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Andesine is a variety of Albite and a member of the Feldspar Group of minerals that includes Albite, Amazonite, Andesine, Anorthite, Bytownite, Hyalophane, Labradorite, Moonstone, Oligoclase, Orthoclase, Sanidine and Sunstone. Andesine is an intermediate member of the Plagioclase Feldspars in a solid solution series between Albite and Anorthite and close to Labradorite. It is a common rock building mineral but crystals are rare.

Andesine was named in 1841 by Otto Wilhelm Herman von Abich (1806–1886) for the Andes Mountains of South America where it is abundant in the lavas.

Sources of gem quality Andesine crystals are from recent finds in Congo, China and Tibet. A small find in 2002 in the Goma area of the Democratic Republic of Congo produced a relatively small quantity of beautiful red, green and yellow gems. The China Andesine is not as intense red as the Congo material, more of an orangish-red. Another find of gem quality crystals occurred in Tibet in 2005. This material, also called Tibet Sunstone, is more of a yellow to greenish-yellow base color with weak to strong coppery overtones. The Tibet Andesine has very different look from the intense red of the Congo Andesine, but still makes very beautiful and unique gems.

Andesine gems for sale: