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Formula: (Ca,Na)0.3(Mg,Fe)3(Si,Al)4O10(OH)2.4H2O
Phyllosilicate (sheet silicate), smectite group, forms a series with
beidellite
Crystal System: Monoclinic
Specific gravity: 2.24 to 2.30 measured
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
Environments:
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).
Localities
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).
Alteration
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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