CAVANSITE
The large stilbite-heulandite plate shown below has
dozens of nice, subspherical masses of dark blue cavansite
crystals. Cavansite is a rare mineral first described in the literature
in the late 1960s based on a minor occurrence in Oregon. In the early
1970s, high-quality, richly colored cavansite was found in quarries of western
India (near Ahmadnagar, Poona District, Maharashtra State). The specimen shown
below is from there.
Cavansite is a hydrous calcium vanadosilicate
(Ca(VO)Si4O10·4(H2O)). In western India,
it occurs as a secondary mineral filling voids in breccias & basalts in the
Deccan Traps succession, a Cretaceous-Tertiary boundary-aged (65 m.y.) flood
basalt deposit.
Cavansite has a glassy, nonmetallic luster, bluish
color, bluish streak, a hardness of 3 to 4, has cleavage, and conchoidal
fracture.
Cavansite blueberries (~1-2 cm in size) on plate of stilbite and heulandite from
western India (CM public display, Carnegie Museum of Natural History, Pittsburgh,
Pennsylvania, USA).
Some info. from:
Mookherjee & Phadke (1998) - Gondwana
Geological Magazine 13(2): 23-27.
Powar & Byrappa (2001) - Journal of
Mineralogical and Petrological Sciences 96: 1-6.