SERPENTINE, in mineralogy the name for a group of min erals of the composition probably crystallizing in the rhombic system. According to the habit and optical proper ties of the crystals, varieties are known under different names, the fibrous types including chrysotile, metaxite and picrolite and a platy variety is known as antigorite. The hardness is and the density 2.5-2.7. The dominant cleavage is parallel to the fibres or plates. The colour of the minerals is usually green, but is de pendent on the content of iron, colourless, red and yellow serpen tines being known.
Serpentine is a common alteration product of magnesium sili cates, particularly of olivine, and the rhombic and monoclinic pyroxenes. In igneous rocks it is believed to arise during a late pneumatolytic or hydrothermal stage of their consolidation. In metamorphic rocks the mineral is frequently met with as an alteration product of the olivine forsterite, less often of diopside, as in marbles and lime-silicate rocks.
The variety antigorite appears to be essentially a metamorphic mineral, the original mineral coming from the Antigorio valley in Piedmont. Chrysotile serpentine often fills veins and seams in massive serpentine rocks and then displays a well-marked fibrous structure, with the fibres arranged transverse to the veins. The asbestos of commerce is largely chrysotile and is derived both from igneous rocks and metamorphosed dolomites.
In petrology the name serpentine is given to those rock masses which consist essentially of serpentine. The purest are derived from peridotites or dunites. In these as in other varieties the serpentine is frequently found as definite pseudomorphs after olivine, enstatite, augite or hornblende, and the mineral may show a characteristic arrangement indicative of the parent mineral. Thus serpentine derived from olivine frequently possesses a mesh structure, from monoclinic pyroxene, a knitted structure, from hornblende, a lattice structure, while the serpentine pseudomorphs of the rhombic pyroxenes are known as bastite.
Serpentines are largely used as ornamental stones. The beauty and variety of these rocks are due to the veining and mottling of the massive serpentine by talc, magnesite, iron oxide and indi vidual crystals of schillerized pyroxenes. Serpentines of igneous origin are widely distributed. In the British Isles the largest masses occur at the Lizard in Cornwall and in the Shetland Isles. They are well developed in the Alps, Pyrenees and Urals, in North America, and occupy a large area of New Caledonia. In Australia, a linear belt of serpentine intrusions can be traced in north-eastern New South Wales over a distance of 200 miles.
The rock known as ophicalcite is an intimate mixture of calcite and serpentine, resulting from the metamorphism of an impure dolomitic limestone. The well-known "eozoon marble" of Canada and the serpentine marble of Connemara are of this character.
For serpentine in geometry see CURVE, SPECIAL. (C. E. T.) a town of Russia, in the province of Mos cow, in 54° 56' N., 28' E. Built on high cliffs on both banks of the river Nara, 3 m. above its confluence with the Oka, Serpukhov is an important manufacturing and commercial town. Pop. (1933) 77,50o. It has important textile and dyeing indus tries, and its chintz is famous. There are also iron and copper foundries. Grain, hemp and timber, brought from the east down the Oka, are discharged at Serpukhov and sent on to Moscow and Leningrad. The cathedral (138o) was rebuilt in the 18th century; the old fortress has almost entirely disappeared.
Serpukhov is one of the oldest towns of the principality of Moscow; in 1328 it was a nearly independent principality under the protectorate of Moscow. Its fortress protected Moscow on the south and was often attacked by the Tatars ; the Mongol prince Toktamish plundered it in 1382, and the Lithuanians in 141o. In 1556 the town was strongly fortified, so that fifteen years later it was able to resist the Mongols. Its commercial importance dates from the 18th century.