Copper, again, forms a number of minerals, and the chief is the red oxide of the metal, called cuprite. It crystallizes in the cubic system. Its colour is red, and tinges a flame green. Cuprite yields excellent copper, and is found in Cornwall, and in many places on the continent. The black oxide is rarely found. It is known as melaconite.
Malachite (carbonate of copper) is remarkable for its beautiful green colour. In Australia it is worked for copper. It is chiefly ornamental. Siberia yields the finest specimens, but the mineral is found in Cornwall and Cumberland, as well as on the continent. Chessylite (from Chessy, in France) is frequently found with malachite. It has been called blue malachite, or the azure copper ore. It is used as a paint.
Besides the above, copper unites with sulphur to form minerals, such as the needle ore (bismuthic sulphide of copper), antimonial sulphide, bournonite; purple copper, and copper pyrites, which is very abundant, and furnishes us with most of our copper. There is also the “grey” copper ore, which contains various metals; even silver is obtained from it at times.
Bismuth gives us only a few minerals, of secondary importance. Native bismuth resembles antimony, but is reddish in hue. Bismuth ochre, bismuth blende, and bismuthine are the chief combinations.
Lead is more important, and is obtained from galena, the sulphide of lead, which is very abundant, and the principal lead ore. It can be at once distinguished by its high specific gravity and metallic lustre; the “cubic cleavage” also is very easy. It frequently is found containing silver, and even gold, antimony, iron, etc. There are several suphantimonites of lead, such as zinkenite, geocronite, etc., and the salts, such as sulphate of lead and white lead ore, or carbonate of lead (cerasite). The chromate of lead is found in the Ural Mountains.
Tin is not found in a native state, but as tinstone, or binoxide of tin, named cassiterite. It is found largely in Cornwall, and the mines there have yielded great quantities for generations. Tin pyrites, a union of sulphides of tin, iron, and copper, is also found in Cornwall.
Zinc is produced from the ore called (zinc) blende, or sulphide of zinc (black Jack). Its colour is very variable, sometimes red, but when pure is greenish-yellow. It is also found black and brown. The red oxide of zinc (or spartalite) is also worked for zinc. The carbonate, or zinc spar, is common, and used to make brass, as is calamine, which is possessed of a remarkable lustre, and is even luminous when rubbed. It is a silicious oxide of zinc, and is found in the sedimentary rocks. When heated, it displays strong electric properties.
Chromium occurs in very few mineral combinations; chromate of lead, chrome iron, and chrome ochre, or sesqui-oxide of chromium are the only important ones.
Antimony minerals are very hard; the tersulphide is the most common, and from this the metallic antimony is produced. Red antimony, the oxide, is a rarer ore.
Arsenic resembles antimony, and occurs in combination with many metals. White arsenic, or arsenious acid, is found in Bohemia, Alsace, Transylvania, etc. Orpiment and realgar are sulphides of arsenic, and are employed as colouring matters in paint and fireworks. Arsenic is very poisonous.