공작석(말라카이트) Malachite

원산지 : Kolwezi, Zaire

Dims: 11.7 x 8.9 x 4.3 cm

Though this large chunk of Malachite is not shaped or polished very well, it is still very attractive as a decorative piece, and generous as part of a lapidarist's supply. The cutting job that it has accentuates a few botryoidal formations that the rough material originally had, but most are ground smooth. It has the classic green coloration of all Malachite, and shows excellent color zonation, with the contrast of alternating pale and deep green bands in concentric patterns. A substantial portion of the piece is not polished at all, and shows flat, sawn faces that have not been ground down. This unpolished area also shows many crevices that extend into the piece; looking into these crevices, one can see botryoidal or maybe even stalactitic forms that the natural Malachite has taken. Even though (or maybe because) this specimen hasn't been finished, something about it is very attractive to me... it is probably the lapidarist in me, thinking about what I could make out of it.

THE MINERAL MALACHITE

·    Chemistry: Cu₂(CO₃)(OH)₂, Copper Carbonate Hydroxide.

·    Class: Carbonate

·    Uses: As mineral specimens, an important ore of copper, as an ornamental stone, a pigment and for jewelry.

THE PHYSICAL CHARACTERISTICS OF MALACHITE:

·   Color is banded light and dark green or (if crystalline), just dark green.

·   Luster is dull in massive forms and silky as crystals.

·   Transparency is opaque in massive form and translucent in crystalline forms.

·   Crystal System is monoclinic; 2/m.

·   Crystal Habitsin its massive forms are botryoidal, stalactitic or globular. Crystals are acicular or fibrous and form in tufts and encrustations. Frequently found as pseudomorphs of azurite.

·   Cleavage is good in one direction but rarely seen.

·   Fracture is conchoidal to splintery.

·   Hardness is 3.5-4.

·   Specific Gravity is 3.9+ (slightly heavy).

·   Streak is green.

·   Other Characteristics: Weakly effervesces in acid.

·   Associated Minerals include limonite, chalcopyrite, bornite, native copper, calcite, cuprite, azurite, chrysocolla and many rare copper minerals such as kolwezite, shattuckite, antlerite, brochantite, graemite, aurichalcite, sphaerocobaltite, atacamite, chalcophyllite, conichalcite, rosasite, chalcosiderite, clinoclase, cornetite, duftite, libethenite, liroconite, mixite and mottramite among others.

·   Notable Occurrences include many classic mineral localities such as Shaba, Congo; Tsumeb, Nambia; Ural mountains, Russia; Mexico; several sites in Australia; England and several localities in the Southwestern United States especially in Arizona, USA.

·   Best Field Indicators are color banding, softness, associations and reaction to acid.