itriol (see IRON).

COPPER-GLANCE, a mineral consisting of cuprous sulphide, Cu2S, and
crystallizing in the orthorhombic system. It is known also as
chalcocite, redruthite and vitreous copper (German, _Kupferglaserz_ of
G. Agricola, 1546). The crystals have the form of six-sided tables or
prisms; the angle between the prism faces (lettered o in the figure)
being 60 deg. 25'. When twinned on the prism planes o, as is frequently
the case, the crystals simulate hexagonal symmetry still more closely,
as in the minerals aragonite and chrysoberyl. Twinning also takes place
according to two other laws, giving rise to interpenetrating crystals
with the basal planes (s) of the two individuals inclined at angles of
69 deg. or 87 deg. 56' respectively. The mineral also occurs as compact
masses of considerable extent. The colour is dark lead-grey with a
metallic lustre, but this is never very bright, since the material is
readily altered, becoming black and dull on exposure to light. The
mineral is soft (H.=2-1/2) and sectile, and can be readily cut with a
knife, like argentite; sp. gr. 5.7. Analyses agree closely with the
formula Cu2S, which corresponds to 79.8% of copper; small quantities of
iron and silver are sometimes present.

[Illustration]

Next to chalcopyrite, copper-glance is the most important ore of copper.
It usually occurs in the upper part of the copper-bearing lodes, and is
a secondary sulphide derived from the chalcopyrite met with at greater
depths; sometimes, however, the two minerals are found together in the
same part of the lodes. The best crystals are from St Just, St Ives, and
Redruth in Cornwall, and from Bristol in Connecticut. Small crystals of
recent formation are found on Roman bronze coins in the thermal springs
at Bourbonne-les-Bains.

Copper-glance readily alters to other minerals, such as malachite,
covellite, melaconite and chalcopyrite. On the other hand, it is found
as pseudomorphs after chalcopyrite, galena, and organic structures such
as wood; copper-glance pseudomorphous after galena preserves the
cleavage of the original mineral and is known as harrisite.

Isomorphous with copper-glance is the orthorhombic mineral stromeyerite,
a double copper and silver sulphide, CuAgS, which occurs in abundance in
the Altai Mountains. (L. J. S.)

COPPERHEADS, an American political epithet, applied by Union men during
the Civil War to those men in the North who, deeming it impossible t