Saponite

Saponite is a trioctahedral mineral of the smectite group. Its chemical formula is Ca0.25(Mg,Fe)3((Si,Al)4O10)(OH)2·n(H2O).[2] It is soluble in sulfuric acid. It was first described in 1840 by Svanberg. Varieties of saponite are griffithite, bowlingite and sobotkite.

Saponite
Saponite (light green) mixed with chamosite (dark green) and copper
General
CategoryPhyllosilicates
Smectite group
Formula
(repeating unit)		Ca0.25(Mg,Fe)3((Si,Al)4O10)(OH)2·n(H2O)
Strunz classification9.EC.45
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m
Unit cella = 5.3 Å, b = 9.14 Å
c = 16.9 Å; β = 97°; Z = 2
Identification
ColorWhite, yellow, red, green, blue
Crystal habitGranular - Massive
Cleavage{001} perfect
TenacityBrittle dry, plastic when hydrated
Mohs scale hardness1.5
LusterGreasy, dull
StreakWhite
DiaphaneityTranslucent
Specific gravity2.24 - 2.30
Optical propertiesBiaxial (-)
Refractive indexnα = 1.479 - 1.490 nβ = 1.510 - 1.525 nγ = 1.511 - 1.527
Birefringenceδ = 0.032 - 0.037
PleochroismX = colorless, light yellow to green-brown; Y = Z = colorless, greenish brown to dark brown
2V angleCalculated: 20° to 26°
References[1][2][3]

It is soft, massive, and plastic, and exists in veins and cavities in serpentinite and basalt. The name is derived from the Greek sapo, soap. Other names include bowlingite; mountain soap; piotine; soapstone.

Occurrence

Saponite was first described in 1840 for an occurrence in Lizard Point, Landewednack, Cornwall, England.[2] It occurs in hydrothermal veins, in basalt vesicles, skarns, amphibolite and serpentinite. Associated minerals include celadonite, chlorite, native copper, epidote, orthoclase, dolomite, calcite and quartz.[3]

Saponite is found in Ząbkowice Śląskie in Silesia, Svärdsjö in Dalarna, Sweden and in Cornwall, UK. The soap stone of Cornwall is used in the porcelain factory. Saponite is also found in the "dark rims" of chondrules in carbonaceous chondrites and seen as a sign of aqueous alteration.[4]

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See also

References
  1. Webmineral data
  2. Mindat.org
  3. Handbook of Mineralogy
  4. Zolensky, Michael; Barrett, Ruth; Browning, Lauren (July 1993). "Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites". Geochimica et Cosmochimica Acta. 57 (13): 3123–3148. Bibcode:1993GeCoA..57.3123Z. doi:10.1016/0016-7037(93)90298-B.

This article contains material from the U.S. Bureau of Mines Dictionary of Mining, Mineral, and Related Terms.

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