BROMLITE  , a member of the

aragonite group of minerals . It consists of an isomorphous mixture of calcium and barium carbonates in various proportions, (Ca, Ba) CO3, and thus differs chemically from barytocalcite (q.v.) which is a double salt of these carbonates in equal molecular proportions . Being isomorphous with aragonite, it crystallizes in the orthorhombic system, but simple -crystals are not known . The crystals are invariably complex twins, and have the form of doubly terminated pseudo-hexagonal pyramids, like those of witherite but more acute; the faces are horizontally striated and are divided down their centre by a twin-suture, as represented in the adjoining figure . The examination in polarized light of a transverse section shows that each compound crystal is built up of six differently orientated individuals arranged in twelve segments . The crystals are translucent and white, sometimes with a shade of pink . Sp. gr . 3.706; hardness 4-41 . The mineral has been found at only two localities, both of which are in the north of England . At the Fallowfield lead mine, near Hexham in Northumberland, it is associated with witherite; and at Bromley Hill, near Alston in Cumberland, it occurs in veins with galena . The species was named bromlite by T . Thomson in 1837, and alstonite by A .

Breithaupt in 1841, both of which names, derived from the locality, have been in

common use . (L . J .