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Encyclopedia Britannica

COPPERMINE

This article appears in Volume V07, Page 111 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: COM-COR

COPPERMINE , a river of Mackenzie

district

DISTRICT

, Canada, about 475 M. long, rising in a small, lake in approximately I ro 2o' W. and 65 5o' N., and flowing south to Lake Gras and then north-westward to Coronation Gulf in the Arctic Ocean. Like Back's river, the only other large river of this part of Canada, it is unnavigable, being a succession of lakes and violent rapids. The country through which it flows is a mass of low hills arid morasses. The river was discovered by Samuel Hearne in 1771, and was explored from Point Lake to the sea by Captain (after-wards Sir John) Franklin in 1821.
COPPER-PYRITES, or CHALCOPYRITE, a copper iron sulphide (CuFeS2), an important ore of copper. The name copper-pyrites is from the Ger. Kupferkies, which was used as fpr back as 1546 by G. Agricola; chalcopyrite (from xaArcos, " copper," and pyrites) was proposed by J. F. Henckel in his Pyritologia, oder Kiess-Historie (1725). By the ancients copper-pyrites was included with other minerals under the term pyrites, though the copper-ore from Cyprus referred to by Aristotle as chalcites may possibly have been identical with this

mineral

MINERAL

.
Chalcopyrite crystallizes in the tetragonal system with inclined
hemihedrism, but the form is so nearly cubic that it was not
recognized as tetragonal until accurate measurements were
made in 1822. Crystals are usually tetrahedral in aspect, owing
to the large development of the sphenoid P {111}. The faces
of this form are dull and striated, whilst the smaller faces of the
complementary sphenoid P' {III} (fig. 1) are

bright

BRIGHT, JOHN (1811-188g)
BRIGHT, SIR CHARLES TILSTON

and smooth.
The combination of these two forms produces a figure resembling
an

octahedron

OCTAHEDRON (Gr. 6K-rw, eight, Mpa, base)

, the
angle between P and
P' being 70 7k',
corresponding to the
angle 700 32' of the
regular

octahedron

OCTAHEDRON (Gr. 6K-rw, eight, Mpa, base)

.
The other faces
shown in fig. r are
the basal pinacoid,
a fool}, and two
square pyramids,
b { IoI } and c 1201). Crystals are usually twinned, and are often complex and difficult to decipher. There are three twin-laws, the twin-planes being (III), (tor) and Oro) respectively. Twinning according to the first law is effected by rotation about an

axis

AXIS (Lat. for " axle ")

normal to the sphenoidal face (III), the resulting form resembling the twins of blende and spinel. Twinning according to the second law can only be explained by reflection across the plane (ror), not by rotation about an

axis

AXIS (Lat. for " axle ")

; chalcopyrite affords an excellent example of this comparatively rare type of symmetric twinning. Interpenetration twins (fig. 2) with (1 ro) as twin-plane are of very rare occurrence.
Crystals have imperfect cleavages parallel to the eight faces of the pyramid c 12011. The fracture is conchoidal, and the material is brittle. Hardness 4; specific gravity 4.2. The colour is brass-yellow, and the lustre metallic; the streak, or colour of the powder, is greenish-black. The

mineral

MINERAL

is especially liable to surface alteration, tarnishing with beautiful iridescent colours; a blue colour usually predominates, owing probably to the alteration of the chalcopyrite to covellite (CuS). The massive and compact mineral frequently exhibits this iridescent tarnish, and is consequently known to miners as " peacock ore " or " peacock copper." The massive mineral sometimes occurs in mammillary and botryoidal forms with a smooth brassy surface, and is then known to Cornish miners as " blistercopper-ore."
Chalcopyrite or copper-pyrites may be readily distinguished from iron-pyrites (or pyrites), which it somewhat resemblesin appearance, by its deeper colour and lower degree of hardness: the former is easily scratched by a knife, whilst the latter can only be scratched with difficulty or not at all. Chalcopyrite is decomposed by nitric acid with separation of

sulphur

SULPHUR

and formation of a green solution; ammonia added in excess to this solution changes the green colour to deep blue and precipitates red ferric hydroxide.
The chemical

formula

CuFeS2 corresponds with the percentage composition Cu =34'5, Fe =30'5, S = 35.0. Analyses usually, however, show the presence of more iron, owing to the intimate admixture of iron-pyrites. Traces of gold, silver, selenium or thallium are sometimes present, and the mineral is sometimes worked as an ore of gold or silver.
Chalcopyrite is of wide distribution and is the commonest of the ores of copper. It occurs in metalliferous veins, often in association with iron-pyrites, chalybite, blende, &c., and in

Cornwall

CORNWALL

and Devon, where it is abundant, with cassiterite. The large deposits at Falun in Sweden occur with serpentine in gneiss, and those at Montecatini, near Volterra in the province of Pisa, serpentine and gabbro. At Rammelsberg in the Harz it forms a bed in argillaceous schist, and at Mansfield in Thuringia it occurs in the Kupferschiefer with ores of nickel and

cobalt

COBALT (symbol Co, atomic weight 59)

. Extensive deposits are

mined

MINED

in the United States, particularly at Butte in Montana, and in Namaqualand, South Africa. Well-crystallized specimens are met with at many localities; for example, formerly at Wheal Towan (hence the name towanite, which has been applied to the species) in the St Agnes

district

DISTRICT

Cornwall

CORNWALL

, at Freiberg in Saxony, and Joplin, Missouri. (L. J. S.)

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