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Pirssonite

Discovered in 1896; IMA status: Valid (pre-IMA; Grandfathered).

Chemistry

Chemical Formula:

Na₂Ca(CO₃)₂·2(H₂O)

Hydrated Sodium Calcium Carbonate

Molecular Weight:

242.11 gm

Composition:

Sodium

18.99 %

Na

25.60 %

Na₂O

Calcium

16.55 %

Ca

23.16 %

CaO

Hydrogen

1.67 %

H

14.88 %

H₂O

Carbon

9.92 %

C

36.36 %

CO₂

Oxygen

52.87 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Carbonates

Strunz 8th Ed. ID:

5/D.02-50

Nickel-Strunz 10th Ed. ID:

5.CB.30

5 : CARBONATES (NITRATES)
C : Carbonates without additional anions, with H₂O
B : With large cations (alkali and alkali-earth carbonates)

Related to:

Thermonatrite - Chalconatronite Series

Crystal Data

Crystallography:

Orthorhombic - Pyramidal

Crystal Habit:

Hemimorphic crystals, to 2 cm; granular, massive, may be as efflorescences.

Twinning:

None

Physical Properties

Cleavage:

None

Fracture:

Conchoidal

Tenacity:

Brittle

Hardness (Mohs):

3.0 - 3.5

Density:

2.352 - 2.382 (g/cm³)

Luminescence:

Fluorescent and Phosphorescent; SW UV = weak blue-white to blue-gray

Radioactivity:

Not Radioactive

Other:

Pyroelectric; with the end of the [001] axis terminated by {131} becoming negatively electrified on cooling. Soluble in H2O, leaving CaCO3.

Optical Properties

Color:

Colorless, Grayish, White

Transparency:

Transparent to Translucent

Luster:

Vitreous

Refractive Index:

1.5043 - 1.5751  Biaxial ( + )

Birefringence:

0.0708

Dispersion:

Relatively Weak; r < v

Pleochroism:

None

Occurances

Geological Setting:

A rare component of saline lake-bed sediments; in a differentiated alkalic massif.

Common Associations:

Gaylussite, Northupite, Trona, (Borax Lake, California, USA); Bradleyite, Gaylussite, Northupite, Shortite, Trona (John Hay, Jr. Well No. 1, Wyoming, USA).

Common Impurities:

n/a

Type Locality:

Searles Lake, San Bernardino County, California, USA

Year Discovered:

1896

View mineral photos:

Pirssonite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Pirssonite was named to honor Professor Louis Valentine Pirsson (1860–1919), American petrographer and mineralogist, Professor of Physical Geology at Yale University, New Haven, Connecticut, USA.

Pirssonite is one of several carbonate minerals that form in non-marine evaporite deposits. Other evaporite carbonates include Trona, Gaylussite, Northupite, Nahcolite and Thermonatrite. Evaporite minerals are geologically important because they clearly are related to the environmental conditions that existed at the time of their deposition, namely arid. They also can be easily recrystallized in laboratories in order to confirm their specific characteristics of formation.

Chemically, Pirssonite and Gaylussite differ only in their number of water molecules, yet their symmetries are quite different. This is an indication of a change in their respective crystal structures. The two are best distinguished by their crystal habits in which Pirssonite has a distinctive tabular diamond-shaped crystal form. Pirssonite can lose its water molecules and specimens should be stored in a sealed container.

Distribution: in the USA, the type locality at Searles Lake, San Bernardino County, California; also in California at Borax Lake, Lake County, in Deep Spring Lake, Inyo County, and at Owens Lake, Mono County; in the John Hay, Jr. Well No. 1, about 30 km west of Green River, Sweetwater County, Wyoming. On the Arizaro, Pastos Grandes, and Pozuelos playas, Salta Province, Argentina. From the Jequetepeque River Valley, northwest Peru. On the Otjiwalundo Salt Pan, about 400 km west-northwest of Otavi, Namibia. In the Beypazari Basin, Ankara, Turkey. On Mt. Kukisvumchorr, Khibiny massif, and Mt. Alluaiv, Lovozero massif, Kola Peninsula, Russia.

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