saponite

{{Infobox mineral | name = Saponite | category = Phyllosilicate minerals | group = Smectite group | boxwidth = | image = Chamosite, Saponite, Copper-188771.jpg | imagesize = 260px | caption = Saponite (light green) mixed with chamosite (dark green) and copper | formula = | IMAsymbol = Sap | strunz = 9.EC.45 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/m | unit cell = a = 5.3 Å, b = 9.14 Å c = 16.9 Å; β = 97°; Z = 2 | color = White, yellow, red, green, blue | habit = Granular – Massive | twinning = | cleavage = {001} perfect | fracture = | tenacity = Brittle dry, plastic when hydrated | mohs = 1.5 | luster = Greasy, dull | streak = White | diaphaneity = Translucent | gravity = 2.24–2.30 | density = | polish = | opticalprop = Biaxial (−) | refractive = nα = 1.479 – 1.490 nβ = 1.510 – 1.525 nγ = 1.511 – 1.527 | birefringence = δ = 0.032 – 0.037 | pleochroism = X = colorless, light yellow to green-brown; Y = Z = colorless, greenish brown to dark brown | 2V = Calculated: 20° to 26° | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }} Saponite is a trioctahedral mineral of the smectite group. Its chemical formula is . It is soluble in sulfuric acid. It was first described in 1840 by Svanberg. Varieties of saponite are griffithite, bowlingite and sobotkite.

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.