PHYSICAL PROPERTIES OF MINERALS. 101
both
poles of the needle; or polar, when one part attracts, and another
repels the same pole. Some magnetic iron ores, or natural magnets,
possess polar magnetism; while the common varieties, meteoric iron,
magnetic pyrites, precious garnet, and other minerals, are simply
magnetic. Most minerals "are only attracted by the magnet, but do not
themselves attract iron.
Smell, taste,, and touch furnish
a few characters of minerals. Most have no smell, but some give out a
peculiar odor when rubbed : as quartz, an empyreumatic odor, or smell
of burning; fluor spar, of chlorine; clay, of clay; some limestones and
marls, of bitumen, or a fetid odor. Aluminous minerals acquire a smell
when breathed on. Other odors caused by heat, and often highly
characteristic, are noticed under tests by the blowpipe.
Taste is
produced by all the salts soluble in water. Some are saline, like
common salt; sweetish astringent, like alum; astringent like blue
vitriol; bitter, like epsom salts; cooling, like saltpetre; pungent,
like sal-ammoniac; alkaline, like soda; acid or sour, like sassoline,
&c.
Touch.—Some
minerals are distinguished by a greasy feeling, like talc; others feel
meagre, like clay; others cold. The last character readily
distinguishes true gems from their imitations in glass.
