Travertine
is a form deposited by springs and streams. The name is derived from
Lapis Tiburtinus of Pliny, much of the material being found near
Tivoli. It shows the same banded structure.
288. Malachite.
The
Malachites of Pliny were not our Malachite, but his Smaragdus Medicus
has been identified by King as the mineral now under consideration, and
the Chrysocolla of Theophrastus seems to have been Malachite in part.
In the time of De Boot it was held in great esteem for variou medicinal
properties attributed to it—virtues which had previously been held to
belong to a variety of Jasper, but which were by the magicians
transferred to Malachite, when that particular Jasper could not be
obtained. It is of a rich bright green in colour, some varieties being
banded with lighter and darker greens. The massive botyroidal variety,
chiefly used as an ornamental stone, has a lustre that may be silky
when the fibrous structure is marked, or waxy when very compact. The
crystals, which are usually very minute, are adamantine or vitreous in
lustre. It is translucent to opaque; when heated it turns black and
readily fuses. The specific gravity is high, 3-71 to 4"01. The crystalline form is mono-symmetric, the crystals are minute and acicular.
It
occurs as a decomposition product of copper ores, and is often found in
pseudomorphs of the minerals Cuprite and Azurite. It is associated with
the closely related mineral Azurite in most cases; although it may be
found in any copper-bearing vein, whose contents have undergone
alteration, and as an alteration product of the disseminated
