ACHITE, or AEGIRITE

This article appears in Volume V01, Page 149 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: A10-ADA

ACHITE, or AEGIRITE , a

mineral

MINERAL

of the pyroxene (q.v.) group, Which may be described as a soda-pyroxene, being essentially asodium and ferric metasilicate, NaFe(SiOs)2. In its crystallographic characters it is close to

ordinary

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

pyroxene (augite and

diopside

DIOPSIDE

), being monoclinic and having nearly the same

angle

ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form, angus, 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

between the prismatic cleavages. There are, however, important differences in the optical characters: the birefringence of acmite is negative, the pleochroism is strong and the extinction

angle

ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form, angus, 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

on the plane of symmetry measured to the vertical

axis

AXIS (Lat. for " axle ")

is small (3-5). The hardness is 6-0, and the specific gravity 3'55. Crystals are elongated in the direction of the vertical

axis

AXIS (Lat. for " axle ")

, and are blackish green (aegirite) or dark brown (acmite) in colour. Being isomorphous with augite, crystals intermediate in composition between augite or

diopside

DIOPSIDE

and aegirite are not uncommon, and these are known as aegirine-augite or aegirinediopside.
Acmite is a characteristic constituent of igneous rocks

rich

in soda, such as nepheline-syenites, phonolites, &c. It was first discovered as slender crystals, sometimes a foot in length, in the pegmatite veins of the granite of Rundemyr, near

Kongsberg

KONGSBERG

in Norway, and was named by F. Stromeyer in 1821 from the Gr. aKo, a point, in allusion to the pointed terminations of the crystals. Aegirite (named from Aegir, the Scandinavian sea-god) was described in 1835 from the elaeolite-

syenite

SYENITE

of southern Norway. Although exhibiting certain varietal differences, the essential-identity of acmite and aegirite has

long

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

been established, but the latter and more

recent

RECENT

name is perhaps in more general use, especially among petrologists.

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