h harder (H. = 3-1/2-4) and denser (sp. gr. 2.85) than
calcite. The two minerals may also be readily distinguished by the fact
that dolomite is not acted upon by cold, dilute acids (see below,
_Dolomite Rock_). Crystals of dolomite vary from transparent to
translucent, and often exhibit a pearly lustre, especially when the
faces are curved; the colour is usually white or yellowish.

The crystallized mineral was first examined chemically by P. Woulfe in
1779, and was named compound-spar by R. Kirwan in 1784; other early
names are bitter-spar, rhomb-spar and pearl-spar (but these included
other rhombohedral carbonates). The name dolomite (_dolomie_ of N. T. de
Saussure, 1792) is in honour of the French geologist, D. G. Dolomieu,
who in 1791 noted that certain Tyrolese calcareous rocks and Italian
marbles effervesce only slightly in contact with acid; this name was for
many years applied to the rock only, but was later extended to the
crystallized mineral, first in the form dolomite-spar.

In the white crystalline dolomite-rock of the Binnenthal near Brieg in
Switzerland beautiful water-clear crystals of dolomite are found; and
crystallized masses occur embedded in serpentine, talc-schist and other
magnesian silicate rocks. The best crystallized specimens are, however,
usually found in metalliferous deposits; for example, in the iron mines
of Traversella near Ivrea in Piedmont (as large twinned rhombohedra) and
Cleator Moor in Cumberland; in the deposits of lead and zinc ores at
Alston in Cumberland, Laxey in the Isle of Man, Joplin in Missouri; and
in the silver veins of Schemnitz in Hungary and Guanajuato in Mexico.

Several varieties of dolomite have been distinguished, depending on
differences in structure and chemical composition. Miemite is a
crystallized or columnar variety, of a pale asparagus-green colour, from
Miemo near Volterra in Tuscany; taraspite is a similar variety from
Tarasp in Switzerland. Gurhofite, from Gurhof near Aggsbach in Lower
Austria, is snow-white, compact and porcellanous. Brossite, from the
Brosso valley near Ivrea in Piedmont, and tharandite, from Tharand in
Saxony, are crystallized varieties containing iron. Closely related is
the species ankerite (q.v.). (L. J. S.)

_Dolomite Rock._--The rock dolomite, also known as dolomitic or
magnesian limestone, consists principally of the mineral of the same
name, but often contains admixture of other substances, such as calcite,
quartz, carbo