nd in 1832 F.S. Beudant applied the name ceruse
to the mineral, whilst the present form, cerussite, is due to W.
Haidinger (1845). Popular names in early use were lead-spar and
white-lead-ore.

[Illustration: FIG. 1]

Cerussite crystallizes in the orthorhombic system and is isomorphous
with aragonite. Like aragonite it is very frequently twinned, the
compound crystals being pseudo-hexagonal in form. Three crystals are
usually twinned together on two faces of the prism m{110}, producing
six-rayed stellate groups (figs, 1 and 2) with the individual crystals
intercrossing at angles of nearly 60 deg. Twinning on the faces of the
prism r{130}, the angles of which are also nearly 60 deg., produces a
similar kind of grouping, but is much less common. Crystals are of
frequent occurrence, and they usually have very bright and smooth faces.
The mineral also occurs in compact granular masses, and sometimes in
fibrous forms. It is usually colourless or white, sometimes grey or
greenish in tint; it varies from transparent to translucent, and has an
adamantine lustre. It is very brittle, and has a conchoidal fracture.
Hardness 3-3-1/2; sp. gr. 6.5. A variety containing 7% of zinc
carbonate, replacing lead carbonate, is known as iglesiasite, from
Iglesias in Sardinia, where it is found.

[Illustration: FIG. 2.]

The mineral may be readily recognized by its characteristic twinning, in
conjunction with the adamantine lustre and high specific gravity. It
dissolves with effervescence in dilute nitric acid. Before the blow-pipe
it fuses very readily, and gives reactions for lead. Cerussite occurs in
metalliferous veins in association with galena, and has been formed by
the action of carbonated waters on the galena; it is therefore found in
the upper parts of the lodes together with other secondary minerals,
such as limonite. Finely crystallized specimens have been obtained from
the Friedrichssegen mine near Ems in Nassau, Johanngeorgenstadt in
Saxony, Mies in Bohemia, Phenixville in Pennsylvania, Broken Hill in New
South Wales, and several other localities. Delicate acicular crystals of
considerable length were found long ago in the Pentire Glaze mine near
St Minver in Cornwall. It is often found in considerable quantities, and
contains as much as 77-1/2% of lead. (L. J. S.)

CERUTTI, GIUSEPPE ANTONIO GIACHIMO (1738-1792), French author and
politician, was born at Turin on the 13th of June 1738. He joined the
Society of Jes