MICROCLINE & SCHORL QUARTZ
This is nice medium sized cluster of twin white microcline crystals with a 100 or so small schorl crystals growing around it. Collected by an Argentina geologist friend of mine at Papchacra, Catamarca Province, Belen, Argentina. Crystal piece measures about 60 mm x 55 mm x 35 mm. Specimen has a neat diamond shape to it. I specifically picked out combination specimens on microline. In all cases the matrix for these is dominated by the potassium feldspar - microcline indicating a pegmatitic origin for these.
The feldspar family of minerals presents some of the most diverse, desirable and strikingly beautiful gemstones on earth. Among other factors, the occurrence of feldspar appears to center around the affinity of silicon to alter as a silicate with a wide variety of available elements. It combines with 0, AL, K, NA, CA, Mg, Fe, SR, Ti, BA, Pb, and Ce, to form in either the monoclinic or triclinic system. The most important of these combinations are with 0, AL, K, NA, CA, and BA. Microcline has a perfect cleavage, ranges from six to 6 1/2 on the MOHS SCALE, has uneven fractures, is opaque and has a weak olive green florescence. It is usually cut "en cabochon" and is used primarily in necklace making and for ornaments. When cut as a cabochon, it may display a silver, gold or blue sheen if it contains a foliated structure and is cut in accord with the proper plane.
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