Formula: Ca3Si3O8(OH)2
Sorosilicate (Si2O7 groups)
Crystal System: Triclinic
Specific gravity: 2.89 measured, 2.905 calculated
Hardness: 4½ to 5
Streak: White
Colour: White, beige, colourless, yellow-brown
Luminescence: Fluoresces light orangish pink under long wave UV
Solubility: Slightly soluble in concentrated acids
Common impurities: B,Al,Fe,Mn,Mg,Sr,Ba,Na,H2O

Metamorphic environments


At Staré Ransko, Krucemburk, Havlíčkův Brod District, Vysočina Region, Czech Republic, rosenhahnite is associated with prehnite, xonotlite and pectolite (HOM).

At the type locality, the Rosenhahnite occurrence, Russian River, Cloverdale area, Mendocino county, California, USA, rosenhahnite is primarily a vein-forming mineral in dark grey boulders, one to three feet in diameter. Narrow veinlets less than 3 cm thick of buff to white, massive rosenhahnite transect brecciated, fine-grained metasedimentary rock. Occasionally open spaces within the buff-coloured veinlets contain clear as well as etched, flat tabular crystals of rosenhahnite. One specimen contains hollow opal pseudomorphs after rosenhahnite. Some white massive veinlets consist of a mixture of rosenhahnite, pectolite and xonotlite; others contain rosenhahnite, diopside, garnet and calcite. The calcite partially replaces rosenhahnite and diopside.
The dense, grey host-rock is composed of fine-grained diopside with variable amounts of hydrogrossular, finely fibrous aggregates of tremolite and minor titanite. Specimens may also contain rosenhahnite in the matrix.
Xonotlite occurs as radial acicular aggregates intergrown with rosenhahnite. Crystals of acicular pectolite and equidimensional datolite are attached to crystals of rosenhahnite in cavities and appear to be later than rosenhahnite. A 0.5 mm-thick veinlet of datolite was found cutting veinlets of rosenhahnite in one specimen.
The bedrock in the vicinity of the rosenhahnite locality is a sandstone which is composed essentially of quartz, albite and chlorite with veins of quartz and calcite. Leonhardite coats fractures in some outcrops. This sandstone is in tectonic contact with altered dolerite composed of augite, altered plagioclase, chlorite and quartz with veins of radiating buff prehnite and quartz. Locally breccia zones up to one foot thick occur along the contact between the sandstone and dolerite. Other rocks in the vicinity include serpentinite, chert, hard black shale and blocks of glaucophane schist, all of which contain numerous veinlets, mainly of quartz and calcite, but some rocks also contain veinlets of pectolite, xonotlite, datolite and apophyllite (AM 52.336-351).

At Durham Quarry, Durham, Durham county, North Carolina, USA, rosenhahnite is associated with prehnite, gyrolite, okenite and apophyllite (HOM).

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