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202 QUARTZ FAMILY. greenish-grey, and yellowish-grey. The bluish grey passes into milk-white *, and smalt-blue; the pearl-grey, into pale violet-blue and plum-blue; the greenish-grey, into a colour which is intermediate between grass and apple green; the yellowish-grey passes into honey-yel low *f*, wax-yellow, and ochre-yellow; from this into yellowish-brown, blackish-brown and browriish-black £. The two last-mentioned colours are very dark, and when held between the eye and the light appear blood- red. The colours occur in clouded, striped, dendritic and moss-like delineations. The bluish-grey varieties, in concentric lamellar con cretions, when cut across into thin tables, and held be tween the eye and the light, exhibit an iridescent appear ance, and hence have been named rainbow calcedony. When cut parallel to the concretions, they exhibit ft Clouded delineation. It occurs massive, in blunt-edged pieces, rolled pieces, with smooth surfaces, plates, crusts, balls, (which some times contain water, forming what are called enhydrites, and more rarely, as at Irkutsk, mineral oil), reniform, bo- tryoidal, corralloidal, stalactitical, cellular, witli impres sions, (generally from cubes of fluor-spar), and crystal lised. The * Leucachates of Pliny. Cerachates of Pliny. • * The green and blue varieties are the rarest. M. De Dree mention!! an azure-blue variety, under the nam'c of tapphirinc, and which is much prized on account of its beauty and rarity. It is found in Transylvania) and at Nertscbinski in Siberia*