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Anorthoclase Crystals

The Mineral anorthoclase




Anorthoclase is the intermediary member of the Albite-Sanidine series. It is interesting to note that this mineral series contains two end members crystallizing in different crystal systems. Albite crystallizes in the triclinic system, whereas Sanidine crystallizes in the monoclinic system.

When Anorthoclase forms, its atoms form in a specific arrangement. This arrangement of the atoms forms the crystal structure of the mineral. Depending on the environment it forms in, it will either form a monoclinic or triclinic crystal. If it forms a monoclinic crystal, it leans toward Sanidine in regard to its crystal structure, and if it forms in the triclinic system, it leans toward Albite. (For this reason, Anorthoclase crystals can either be triclinic or monoclinic, although the tendency is usually toward triclinic.) The scientific classification of Sanidine, Anorthoclase, and Albite can only be determined with x-ray analysis. However, certain localities produce known examples of these particular Feldspars, in which case the mineral type can be determined without complex analysis. (Click here for more detailed information on the crystal structure of the Feldspars.)
Chemical Formula (Na,K)AlSi3O8
Composition Sodium potassium silicate, with a varying ratio of sodium to potassium.
Color Colorless, white, cream, yellow, pink, brown, reddish, greenish, gray
Streak White
Hardness 6 - 6.5
Crystal System Triclinic
Crystal Forms
and Aggregates
In well formed crystals, usually prismatic. Crystals frequently form twins. Also as dense aggregates, grainy, and massive.

Click here for more detailed information on the crystal structure of the Feldspars.
Transparency Transparent to opaque
Specific Gravity 2.5 - 2.6
Luster Vitreous
Cleavage 2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal. The cleavage angle is about 90º.
Fracture Conchoidal to uneven
Tenacity Brittle
In Group Silicates; Tectosilicates; Feldspar Group
Striking Features Crystal habits, cleavage, and hardness
Environment High-temperature, sodium-rich igneous environments.
Rock Type Igneous
Popularity (1-4) 2
Prevalence (1-3) 2
Demand (1-3) 2


Anorthoclase ON EBAY
OTHER NAMES
Anorthose




NOTEWORTHY LOCALITIES
Anorthoclase localities are Mt Erebus, Ross Island, Antarctica; Mount Kilimanjaro, Tanzania; Pantelleria Island, Italy; Tjolling, Norway; and Kusukidani, Wakayama Prefecture, Japan. North American localities are Obsidian Cliff in Yellowstone National Park, Wyoming; Franklin, Sussex Co., New Jersey; and Mont Saint-Hilaire, Quebec, Canada.

COMMON MINERAL ASSOCIATIONS
Quartz, Muscovite, Biotite

DISTINGUISHING SIMILAR MINERALS
Albite, Sanidine, Orthoclase, and Microcline - Indistinguishable without x-ray analysis.


anorthoclase PHOTOS
 
ADDITIONAL RESOURCES
 
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