THE MINERAL THENARDITE

  • Chemistry: Na2SO4, Sodium Sulfate.
  • Class: Sulfates
  • Uses: As a source of sodium to produce soda, various uses in the glass and paper industries and as mineral specimens.
  • Specimens
Thenardite is one of several non-marine evaporite Sulfate Class minerals. It is easily dissolvable in water and specimens should be stored with desiccant. Sulfates in general tend to be more soluble than most of the other mineral classes and simple sodium salts, such as thernardite, are always soluble. As one might imagine, thenardite forms in arid regions as a salty precipitate as well as in dry caves and mines as an efflorescence and as a crusty deposit around fumaroles. It is associated with other minerals that form in the deposits of playa lakes.

Thenardite, which is named for the French chemist Louis J. Thenard, has several distinctive properties in addition to its solubility. For one it has a salty taste similar to halite, but the different cleavages and crystal habits make the two minerals quite distinguishable from each other. Thenardite is also generally fluorescent showing a white color in shortwave UV and a yellow-green color in longwave UV. Thenardite also has a distinctive crystal habit in which crystals form a diamond-like shape (such as from a deck of cards). The crystals are generally flattened and are sometimes well formed showing good orthorhombic symmetry. Although not often seen in mineral shops, thenardite is now making a presence with well formed crystal clusters mostly coming from Searles Lake, San Bernardino County, California.

Thenardite specimens should be stored in closed containers as thenardite is only metastable. The specimens will gradually absorb water and convert to the mineral mirabilite. In volcanic caves on Mt. Etna, Italy; thenardite is an early secondary mineral forming the cave's speleothems. But when the temperature of the cave lowers and the humidity rises, the thenardite coverts to mirabilite.

PHYSICAL CHARACTERISTICS:

  • Color is typically gray, white, colorless or brownish white or yellowish white.
  • Luster is vitreous, pearly to resinous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic: 2/m 2/m 2/m.
  • Crystal Habits include tabular, dipyramidal, flattened, diamond-shaped crystals; often intergrown. Twins form arrowhead like crystals and crossed interpenetration twins. Also as crusts, granular and as massive rock forming beds.
  • Cleavage is perfect in one direction (pinacoidal).
  • Fracture is uneven to hackly or splintery.
  • Hardness is 2.5 - 3.
  • Specific Gravity is approximately 2.7 (average for translucent minerals).
  • Streak is white.
  • Other Characteristics: Easily soluble in water, has a salty taste, is fluorescent white in shortwave UV and yellow-green in longwave UV and can color a flame yellow (for sodium).
  • Associated Minerals include halite, mirabilite, gypsum, glauberite, trona, blodite, alunite, picromerite, sborgite, borax and other borate and non-marine evaporite minerals.
  • Notable Occurrences include several California sites such as Searles Lake, San Bernardino County; Soda Lake, San Luis Obispo County; Bertram deposit, Imperial County and Furnace Creek district, Inyo County; as well as Camp Verde Yavapi County in Arizona and sites in Nevada, USA; Espartinas, Madrid Province, Spain; Siberia, Russia; Mt Etna, Sicily, Italy; Chile; Kazakhstan and Canada.
  • Best Field Indicators are crystal habit, environment of formation, associations, cleavage, taste and fluorescence.
THENARDITE specimens:
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THENARDITE specimen thn-1
$ 40.00
Dims: 2.4 x 1.9 x 1.5" (6.0 x 4.8 x 3.9 cm)
Wt: 2.3 oz. (65 g)
Searles Lake, Trona, San Bernardino County, California, U.S.A.
A pale pink Thenardite crust coats the halite base of this hand specimen. The Thenardite is massive, showing no evidence of crystal form, and has a pink color that is paler than that of the halite base. Its luster is essentially dull, and it is translucent or opaque. As it has pseudomorphed from the halite below, it has retained the original shape, including the "hopper effect" of the halite- the halite itself still has very good form.
no photo
thn-1 ($ 40.00)
Searles Lake, Trona, San Bernardino County, California, U.S.A.
THENARDITE specimen thn-2
$ 25.00
Dims: 1.5 x 1.3 x 0.8" (3.8 x 3.2 x 2.0 cm)
Wt: 14 g
Soda Lake, Carrizo Plain, San Luis Obispo County, California, U.S.A.
At least 6 tabular Thenardite crystals are clustered together to make up this small hand specimen. The largest of these crystals has dimensions of 1.0 x 1.0 x 0.4" (2.6 x 2.6 x 1.0 cm), and all appear to be in excellent condition, showing no fresh damage. Their orthorhombic form is quite good, and all have a dull, pale gray color and a waxy luster. They are only dimly transparent at best. A white, powdery substance- likely a decomposition product- coats the less-exposed areas on the cluster, and no base or host material is present.
no photo
thn-2 ($ 25.00)
Soda Lake, Carrizo Plain, San Luis Obispo County, California, U.S.A.
THENARDITE specimen thn-3
$ 30.00
Dims: 2.6 x 2.2 x 1.4" (6.7 x 5.7 x 3.5 cm)
Wt: 1.7 oz. (47 g)
Soda Lake, San Luis Obispo County, California, U.S.A.
At least 30 intergrown Thenardite blades are clustered together to form this hand specimen. These blades reach dimensions of 1.3 x 1.0 x 0.4" (3.2 x 2.6 x 1.0 cm) and are generally in excellent condition, showing almost no damage. Their orthorhombic form is very good, given their intergrowth. All have a dark gray color and a pearly-to-waxy luster, and are translucent to dimly transparent along their edges. There is no host rock present.
no photo
thn-3 ($ 30.00)
Soda Lake, San Luis Obispo County, California, U.S.A.
THENARDITE specimen thn-4
$ 35.00
Dims: 2.0 x 1.9 x 1.5" (5.1 x 4.7 x 3.7 cm)
Wt: 2.0 oz. (57 g)
Soda Lake, San Luis Obispo County, California, U.S.A.
A cluster of at least 10 intersecting Thenardite tablets makes up this small cabinet specimen. These blades reach dimensions of 1.4 x 1.1 x 0.8" (3.7 x 2.8 x 2.1 cm) and are in excellent condition, showing very little damage. All have excellent orthorhombic bladed form. All are colorless but contain numerous black and gray inclusions, making them appear essentially black, and their luster is waxy. There is no host rock present.
no photo
thn-4 ($ 35.00)
Soda Lake, San Luis Obispo County, California, U.S.A.
THENARDITE specimen thn-5
$ 25.00
Dims: 2.6 x 1.7 x 1.0" (6.7 x 4.4 x 2.6 cm)
Wt: 1.3 oz. (38 g)
Soda Lake, San Luis Obispo County, California, U.S.A.
This cluster of Thenardite tablets is in very good condition, though it shows some weathering at one end. It contains tetragonal tabular crystals that reach dimensions of 0.8 x 0.5 x 0.2" (2.0 x 1.2 x 0.5 cm). They have a gray-black color due to intense inclusion and a waxy luster, and show dim transparence along their edges. There is no host rock present.
no photo
thn-5 ($ 25.00)
Soda Lake, San Luis Obispo County, California, U.S.A.
THENARDITE specimen thn-6
$ 40.00
Dims: 2.8 x 2.3 x 2.2" (7.2 x 5.8 x 5.5 cm)
Wt: 4.3 oz. (117 g)
Soda Lake, San Luis Obispo County, California, U.S.A.
This large Thenardite cluster contains at least 10 tabular crystals, all of which are in excellent condition. The largest of these has dimensions of 2.2 x 1.4 x 0.5" (5.5 x 3.6 x 1.2 cm). All have excellent orthorhombic form, though the largest crystals are a bit rougher than the smaller ones. They have a gray-black color that is caused by intensely concentrated inclusions, but all are moderately transparent around their edges. There is no host rock present.
no photo
thn-6 ($ 40.00)
Soda Lake, San Luis Obispo County, California, U.S.A.
 

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