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Andesine was named after its original occurrence in the Andes Mountains of South America. Andesine belongs to the Plagioclase Feldspar group, an
isomorphous solid solution series. Albite is one member,
containing sodium and no calcium. The other end member, Anorthite,
contains calcium and no sodium. Andesine is an intermediary
member of this series. Andesine is considered by some authorities as a
variety of Albite rather than a separate mineral. The acclaimed
Dana's System of
Mineralogy lists Andesine as an individual mineral,
whereas the IMA does not recognize it as individual mineral
species, but rather a calcium-rich variety of Albite. Andesine is the primary feldspar constituent of the igneous rock Andesite. |
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Chemical Formula |
(Na,Ca)Al1-2Si3-2O8 |
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Composition |
Sodium calcium aluminum silicate. The ratio of sodium to calcium is about 7:3. The amount of aluminum atoms are between 1 and 2, and the amount of silicon atoms are between 3 and 2.
In the Plagioclase Feldspar series, Andesine contains between 50 and 70 percent Albite (Ab), and between 30 and 50 percent Anorthite (An). |
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Color |
Colorless, white, cream, yellow, pale green, gray |
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Streak |
White |
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Hardness |
6 - 6.5 |
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Crystal System |
Triclinic |
Crystal Forms
and Aggregates |
Crystals, which are uncommon, are tabular and frequently twinned. Most often massive, grainy, as chunky masses, and as compact crystal groupings. |
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Transparency |
Transparent to translucent |
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Specific Gravity |
2.66 - 2.68 |
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Luster |
Vitreous to pearly |
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Cleavage |
2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal The cleavage angle is about 90º |
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Fracture |
Subconchoidal to uneven |
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Tenacity |
Brittle |
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In Group |
Silicates; Tectosilicates; Feldspar Group |
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Striking Features |
Crystal habits, cleavage, and hardness |
| Environment |
In basalt rock and in andesites, also in metamorphic rocks.
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| Rock Type |
Igneous, Metamorphic |
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Popularity (1-4)
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2 |
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Prevalence (1-3)
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1 |
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Demand (1-3) |
2 |
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There is a new gemstone called Andesine which has recently penetrated the market. Much of the material is Chinese in origin and has been synthetically diffused to enhance color, and is actually produced from Labradorite.
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Andesine is prevalent in volcanic regions throughout the world. Its original locality in the Andes Mountains is the Marmato District, Manizales, Bolivia. Large crystals are found in the San Gabriel Mountains (Los Angeles County), California. Other localities are the Crestmore Quarry, Riverside County, California; Goodall Farm, Sanford, York County, Maine;
Mont Saint Hilaire, Quebec, Canada; and Portland, Victoria, Australia.
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Potassium Feldspar group - Don't exhibit striations on twinned
crystal surfaces, whereas the Plagioclase feldspars do.
Other
Plagioclase Feldspars - Usually cannot be determined by
practical means.
Spodumene - Has a splintery cleavage.
Calcite
- Much lower hardness.
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