Open Adit™ - Orthoclase Datasheet

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Orthoclase (K-Spar) is an important igneous rock forming tectosilicate mineral. It is also known as alkali feldspar and is common in granite and related rocks. Orthoclase is named based on the Greek for "straight fracture," because its two cleavages are at right angles to each other. Twinned crystals are quite common. Orthoclase is a common constituent of most granites and other felsic igneous rocks and is often found in huge crystals and masses in pegmatite veins.

Orthoclase is used in the manufacture of porcelain and as an ingredient of scouring powder. When pearly and opalescent orthoclase is called moonstone and is used in jewelry. These opalescent varieties are known to be an intergrowth of orthoclase and albite called perthite.

Chemistry:

KAlSi₃O₈, Potasium Aluminum Silicate

Class:

Silicates

Subclass:

Tectosilicates

Group:

Feldspar Group

Varieties:

Adularia, Moonstone

Crystal:

Monoclinic

Color:

Colorless, white, yellowish, pinkish, gray, brown, yellow.

Streak:

White

Luster:

Vitreous to pearly

Diaphaneity:

Transparent to translucent

2.5

6 - 6.5

Good

Uneven to Conchoidal

Prismatic and tabular crystals and their combinations, granular, massive.

Luminescence:

Non-fluorescent

Frequency:

Common

Origin:

Magmatic in rhyolites, trachytes, granites, syenites and pegmatites; metamorphic in various rock types, as orthogneisses and migmatites; hydrothermal in the Alpine-type veins, ore veins, and some sediments, also in placers, a typical rock-forming mineral.

Occurence:

Twentynine Palms, California, USA; Marina di Campo, Elba, Italy; Strzegom, Poland; Itrongay, Madagascar; Black hills, South Dakota, USA; Ratnapura, Sri Lanka.

Application:

Ceramic & glass industry, moonstone as a gemstone.

Metaphysical Properties

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