Discovery of Pyrope Spessartite garnets ( Madagascar )Written by Alain Darbellay GGGems
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A day of July 1996 whereas I stopped in a small village in Madagascar, one presented samples of a strange stone to me. At first sight its color could reminds certain zircon, but I quickly identified them as garnet. After some palaver, one led me to place of discovery. I must acknowledge that I already knew inhabitants with whom I tied friendship previous year. On spot, a notch of about one meter fifty in a white color rock had created a not very impressive hole. But, according to its authors, it was particularly painful to produce it with iron bars only . I readily believed them after to be approached to rock. Some particles of this stone to orange - pink-brown reflections remained taken in bedrock. I encouraged my friends to be still sought. The first samples extracted from a not disaggregated leptynite did not exceed 3.15 cts. after cutting. The observation under day light and incandescent light showed a clear difference in color. Its change, from champagne color under daylight, to an intense red for some, or to pink-orange for others is due to chromium and vanadium traces. This characteristic confers an attractive aspect on these gems. Other samples were orange-yellow and did not change a color under various sources of lighting. Unfortunately, very hard and compact rock in this place, did not allow to extract many stones from it, and occurrence was abandoned a few weeks after its discovery.
Opposite, first samples cut in 1996 showing a change of color. Above, an orange malaya found also in primary occurrence. (It does not change a color) This is two years later, exactly in September 1998, that returning in small village, samples more or less similar to those which I make cut in 1996 were found. They were turbid because of fine rain of small bubbles they contained. Their color was definitely more orange than malaya garnets from first occurrence. Indeed, they did not come from same place. This is a little more than one kilometer of distance that elluvionnar deposit was discovered. I was immediately conscious to be witness of a rare moment in career of an impassioned person in precious stones.
Madagascar corundums ( Sapphire & Ruby discovery )Written by Alain Darbellay GGGems
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AL2O3 Sapphire found in a metamorphized limestone. · Crystallographic properties of corundum: Trigonal.c = 1,3630 pp 0 86°4' ; pa1 = 122°26' Macle according to p (1011), often polysynthetic, accompanied by plans of separation, similar plans are also observed according to a1 (0001) unequal break to conchoïdal. Hardness 9. Density 3,95 to 4,1 Refractive index: 1.76 - 1.77 Uniaxial and optically négative.ng = 1,7675; Np = 1,7593 The faces a1 frequently show phenomenon of asterism, generally due to reflexions within separation p. Strong polychromatism , with following maximum ng. · Chemical properties: corundum is composed of pure alumina; its colouring is due to metallic oxide traces or inclusions. The color of sapphire, due to iron and titanium oxide, gives its best effect under daylight. Electric light makes it often dark. The color of ruby, due to chromium oxide, on contrary shows its most luminous red under electric lighting. The Corundum shows in Madagascar two different aspects: 1 stony and opaque crystals. 2 crystals of smaller size often transparent and usable as gem. In Madagascar, stony corundum comes from mica schists metamorphized by granite, as well as granitic veinules endomorphized and more or less deprived of quartz which injects those. Silimanite is a usual satellite of corundum in this type of deposit. One also finds some in eruptive rocks, syenites. Gems are generally found in alluvium, but come either from basaltic slags, or from metamorphized limestones or endomorpheous feldspatic rocks. 1 2 3 4 5 One distinguishes two principal types of corundum in Madagascar: Type I : isoceloedric, more or less acute accompanied or not by a small face a1 (0001) and more rarely by facets p (1011). Represented by figures 1 to 11, but which often become complicated in consequence of irregularity of development of some of their faces and by stacking with parallel axes of a great number of individuals. 6 7 8 9 10 11 12 13 Scalenoedron Stacking with parallel axes, Crystal supporting on one of its bases gutters at contours of face. a small rhombohedron p in parallel position. Type 2: Characterized by association of prism d 1 (1120) at a broad base, with which can associate isosceles ones, among which e 3 is most frequent, as well as rhombohedron p. The base of Malagasy corundum crystals very frequently shows scratches or triangular figures in relief, limited by p. Macle of blue corundum. Translucent violet - pink sapphire