HARMOTOME  , a

mineral of the zeolite group, consisting of hydrous barium and aluminium silicate, H2BaAl2(SiO3)5+5H20 . Usually a small amount of potassium is present replacing part of the barium . The system of crystallization is monoclinic; only complex twinned crystals are known . A common and characteristic form of twinned crystal, such as is represented in the figure, consists of four intercrossing individuals twinned together according to two twin-laws; the compound group resembles a tetragonal crystal with prism and pyramid, but may be distinguished from this by the grooves along the edges of the pseudo-prism . The faces of the crystals are marked by characteristic striations, as indicated in the figure . Twinned crystals of exactly the same kind are also frequent in phillipsite (q.v.) . Crystals are usually white and translucent, with a vitreous lustre . The hardness is 4zf and the specific gravity 2.5 . The name harrnotome (from apµos, " a joint," and TEµvely, " to cut ") was given by R . J. flatly in 1801, and has a crystallographic signification . Earlier names are cross-stone (Ger . Kreuzstein), ercinite, andreasbergolite and andreolite, the two last being derived from the locality, Andreasberg in the Harz .

Morvenite (from Morven in

Argyllshire) is the name given to small transparent crystals formerly referred to phillipsite . Like other zeolites, harmotome occurs with calcite in the amygdaloidal cavities of volcanic rocks, for example, in the dolerites of Dumbartonshire, and as fine crystals in the agate-lined cavities in the melaphyre of Oberstein in Germany . It also occurs in gneiss, and sometimes in metalliferous veins . At Andreasberg in the Harz it is found in the lead and silver veins; and at Strontian in Argyllshire in lead veins, associated with brewsterite (a strontium and barium zeolite), barytes and calcite . (L . J .