ENSTATITE

This article appears in Volume V09, Page 654 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: EMS-EUD

ENSTATITE , a

rock

-forming

mineral

MINERAL

belonging to the group of orthorhombic pyroxenes. It is a magnesium metasilicate, MgSiO3, often with a little iron replacing the magnesium: as the iron increases in amount there is a transition to bronzite (q.v.), and with still more iron to hypersthene (q.v.). Bronzite and hypersthene were known

long

LONG, GEORGE (1800-1879)
LONG, JOHN DAVIS (1838– )

before enstatite, which was first described by G. A. Kenngott in 1855, and named from ivgTaTi S, " an opponent," because the

mineral

MINERAL

is almost in-fusible before the blowpipe: the material he described consisted of imperfect prismatic crystals, previously thought to be scapolite, from the serpentine of

Mount

MOUNT, WILLIAM SIDNEY (1807-1868)

Zdjar near Schonberg in Moravia. Crystals suitable for goniometric measurement were later found in the meteorite which fell at Breitenhach in the Erzgebirge, Bohemia. Large crystals, a foot in length and mostly altered to steatite, were found in 1874 in the apatite veins traversing mica-schist and hornblende-schist at the apatite mine of Kjorrestad, near Brevig in southern Norway. Isolated crystals are of rare occurrence, the mineral being usually found as an essential constituent of igneous rocks; either as irregular masses in plutonic rocks (norite,

peridotite

PERIDOTITE

pyroxenite

PYROXENITE

, &c.) and the serpentines which have resulted by their alteration, or as small idiomorphic crystals in volcanic rocks (trachyte, andesite). It is also a common constituent of meteoric stones, forming with olivine the bulk of the material: here it often forms small spherical masses, or chondrules, with an internal radiated structure.
Enstatite and the other orthorhombic pyroxenes are distinguished from those of the monoclinic

series

SERIES (a Latin word from serere, to join)

by their optical characters, viz. straight extinction, much weaker

double

refraction and stronger pleochroism: they have prismatic cleavages (with an

angle

ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form,
angus
- ANGUS, EARLS OF
, does not occur in Latin; cognate are the Lat. angere, to compress into a bend or to strangle, and the Gr. ayKOS, a bend; both connected with the Aryan root ank-, to

of S8 16') as well as planes of parting parallel to the planes of symmetry in the ,prism-zone. Enstatite is white, greenish or brown in colour; its hardness is 51, and sp. gr. 3.23.3. (L. J. S.)

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