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The Mineral thenardite

Thenardite Floater Crystal

Thenardite is a delicate sulfate mineral that comes from arid dry or saline lake deposits. It is similar to Mirabilite, a chemically similar mineral to Thenardite that, unlike Thenardite, contains water in its structure. Mirabilite is an unstable mineral, and will dehydrate and lose its water when exposed to air, thereby changing to Thenardite. These altered specimens are in fact Thenardite pseudomorphs after Mirabilite. Some of these crystals, especially those of outstanding crystal form, are artificially grown as by-products of borax mining operations.

Thenardite is named after the French chemist Louis Jacques Thenard (1777-1826), a professor at the University of Paris.

Chemical Formula

Na2SO4

Color

White, yellowish, light brown, gray

Crystal System

Orthorhombic

Properties

Streak
White
Hardness
2.5 - 3
Transparency
Transparent to translucent
Specific Gravity
2.7
Luster
Vitreous
Cleavage
1,1 - basal
Fracture
Uneven to hackly
Tenacity
Brittle
Other ID Marks
1) Has a weak salty taste.
2) Slowly soluble in water.
3) Fluorescent white in shortwave ultraviolet light and yellow-green in longwave ultraviolet light; may also be phosphorescent.

Crystal Habits

As intergrown clusters of distorted crystals, oftenbipyramidal in shape. Individual crystals, which are rare, are tabular and short prismatic. Sometimes in well-formed twinned crystals that bisect each other. Also massive, grainy, encrusting, and in coral-like masses.

Additional Information

Composition
Sodium sulfate
In Group
Sulfates; Anhydrous Sulfates
Striking Features
Weak taste and fluorescence
Environment
Dry lakes and saline lakes in evaporite deposits, mainly in arid regions.
Rock Type
Sedimentary

Noteworthy Localities

Thenardite has come from Espartinas, Spain; Mt. Etna, Vesuvius, Italy; the Bilma Oasis, Niger; and Wadi el Natrun, Egypt. In the U.S., it occurs as sharp, twinned crystals in Soda Lake, San Luis Obispo Co., California. Thenardite also occurs in other dry lake deposits in California, including Searles Lake, San Bernardino Co.; Boron, Kern Co.; and Borax Lake, Lake Co. It also has come from the Verde Valley, Yavapai Co., Arizona.

Common Mineral Associations

Halite, Borax, Ulexite, Colemanite

Distingushing Similar Minerals

Glauberite - Less soluble in water, forms different crystals.
Halite - Much saltier taste, occurs in different crystals, has perfect cubic cleavage.

thenardite Photos



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