did not
attempt to return by sea. It had been predicted that he should die when he
met his superior in divination; and the prophecy was fulfilled in the
person of Mopsus, whom Calchas met in the grove of the Clarian Apollo near
Colophon. Having been beaten in a trial of soothsaying, Calchas died of
chagrin or committed suicide. He had a temple and oracle in Apulia.

Ovid, _Metam._ xii. 18 ff.; Homer, _Iliad_ i. 68, ii. 322; Strabo vi. p.
284, xiv. p. 642.

CALCITE, a mineral consisting of naturally occurring calcium carbonate,
CaCO_3, crystallizing in the rhombohedral system. With the exception of
quartz, it is the most widely distributed of minerals, whilst in the
beautiful development and extraordinary variety of form of its crystals it
is surpassed by none. In the massive condition it occurs as large
rock-masses (marble, limestone, chalk) which are often of organic origin,
being formed of the remains of molluscs, corals, crinoids, &c., the hard
parts of which consist largely of calcite.

The name calcite (Lat. _calx_, _calcis_, meaning burnt lime) is of
comparatively recent origin, and was first applied, in 1836, to the
"barleycorn" pseudomorphs of calcium carbonate after celestite from
Sangerhausen in Thuringia; it was not until about 1843 that the name was
used in its present sense. The mineral had, however, long been known under
the names calcareous spar and calc-spar, and the beautifully transparent
variety called Iceland-spar had been much studied. The strong double
refraction and perfect cleavages of Iceland-spar were described in detail
by Erasmus Bartholinus in 1669 in his book _Experimenta Crystalli Islandici
disdiaclastici_; the study of the same mineral led Christiaan Huygens to
discover in 1690 the laws of double refraction, and E.L. Malus in 1808 the
polarization of light.

An important property of calcite is the great ease with which it may be
cleaved in three directions; the three perfect cleavages are parallel to
the faces of the primitive rhombohedron, and the angle between them was
determined by W.H. Wollaston in 1812, with the aid of his newly invented
reflective goniometer, to be 74 deg. 55'. The cleavage is of great help in
distinguishing calcite from other minerals of similar appearance. The
hardness of 3 (it is readily scratched with a knife), the specific gravity
of 2.72, and the fact that it effervesces briskly in contact with cold
dilute acids are also characters of determinative value.