Formula: (Ca,Na)0.3(Mg,Fe)3(Si,Al)4O10(OH)2.4H2O
Phyllosilicate (sheet silicate), smectite group, forms a series with beidellite
Specific gravity: 2.3
Hardness: 1½ to 2
Streak: White
Colour: White, grey-green, bluish, yellow
Solubility: Decomposed or gelatinised by common acids (Dana)
Common impurities: Ti,Mn,Ni,K,P

Metamorphic environments
Hydrothermal environments
Basaltic cavities

Saponite is hydrothermally deposited in mineralised veins and in vesicles in basalt. It is formed in fissures cutting calc-silicates, iron-rich skarn, amphibolite and serpentinite. Associated minerals include other clay minerals, zeolites, K-feldspar variety adularia, sepiolite, celadonite, chalcedony, chlorite, copper, epidote, orthoclase, dolomite, calcite and quartz (HOM, Dana).


At the Willy Wally Gully, Merriwa, Brisbane county, New South Wales, Australia, saponite is ubiquitous and often completely fills vesicles under 0.5 cm across. Where complete infilling has not occurred, the saponite forms thin coatings which act as a substrate for subsequent zeolite mineralisation (AJM 16.2.84).

The type locality is Lizard Point, Landewednack, Cornwall, England, UK.

At Lindsay's Leap, Newcastle, Mourne Mountains, County Down, Ulster, Northern Ireland, UK, saponite has been found as masses on joint planes in the granite associated with zeolites and danalite (M&M).

At Griffith Park, Hollywood, Hollywood Hills, Los Angeles, Santa Monica Mountains, Los Angeles county, California, USA, saponite occurs in basalt as alteration pseudomorphs after olivine and as fillings in vesicles and cracks (AM 99.2234-2250).

In the copper belt in Michigan, USA, saponite was found in quantity in the South Kearsarge Mine, Centennial, Houghton county, and in less abundance in the Ahmeek Mine, Keweenaw county. In the South Kearsarge mine saponite is one of the latest hydrothermal minerals to form, followed only by a last generation of K-feldspar variety adularia. In the Ahmeek Mine it was found chiefly as solid filling of replacement vugs in which it surrounded crystals of copper and quartz; it was also found with copper and epidote crystals in open cavities as small stalactites up to half an inch in length but less than one tenth of an inch in diameter (AM 10.412-418).


Saponite has been found as an alteration product of olivine or plagioclase in submarine and continental basalt. It has also been shown to result from the authigenic (occurring in place) successive alteration of phlogopite to vermiculite to saponite (Dana).

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