, and is
commonly written with sharps in ascending and flats descending. The most
correct method is to write such accidentals as do not involve a change
of key.

CHROMITE, a member of the spinel group of minerals; an oxide of chromium
and ferrous iron, FeCr2O4. It is also known as chromic iron or as
chrome-iron-ore, and is the chief commercial source of chromium and its
compounds. It crystallizes in regular octahedra, but is usually found as
grains or as granular to compact masses. In its iron-black colour with
submetallic lustre and absence of cleavage it resembles magnetite
(magnetic iron-ore) in appearance, but differs from this in being only
slightly if at all magnetic and in the brown colour of its powder. The
hardness is 51/2; specific gravity 4.5. The theoretical formula FeCr2O4
corresponds with chromic oxide (Cr2O3) 68%, and ferrous oxide 32%; the
ferrous oxide is, however, usually partly replaced by magnesia, and the
chromic oxide by alumina and ferric oxide, so that there may be a
gradual passage to picotite or chromespinel. Much of the material mined
as ore does not contain more than 40 to 50% of chromic oxide. In the
form of isolated grains the mineral is a characteristic constituent of
ultrabasic igneous rocks, namely the peridotites and the serpentines
which have resulted from their alteration. It is also found under
similar conditions in meteoric stones and irons. Often these rocks
enclose large segregated masses of granular chromite. The earliest
worked deposits were those in the serpentine of the Bare Hills near
Baltimore, Maryland, U.S.A.; it was also formerly extensively mined in
Lancaster county, Pennsylvania, and is now mined in California, as well
as in Turkey, the Urals, Dun Mountain near Nelson in New Zealand, and
Unst in the Shetlands.

Chrome-iron-ore is largely used in the preparation of chromium compounds
for use as pigments (chrome-yellow, &c.) and in calico-printing; it is
also used in the manufacture of chrome-steel. (L. J. S.)

CHROMIUM (symbol Cr. atomic weight 52.1), one of the metallic chemical
elements, the name being derived from the fine colour (Gr. [Greek:
chroma]) of its compounds. It is a member of the sixth group in the
periodic classification of the elements, being included in the natural
family of elements containing molybdenum, tungsten and uranium. The
element is not found in the free state in nature, nor to any large
extent in combination, occurring chiefl