About the History and Properties of Topaz

Yellow is the colour generally associated with the topaz, yet topaz is sometimes colourless, or may present almost any colour, and beautiful specimens of other colours are often supposed to be some other mineral, so thoroughly identified is this stone with the colour yellow. The sometime popularity of topaz has of late years declined, and a probable reason is the common substitution of other stones for it. Topaz takes its name from Topazios, meaning "to seek"; because the earliest known locality from whence it came was an island in the Red Sea which was often surrounded by fog, and therefore difficult for the local mariners to find.

The name of topaz in mineralogical science is Topaz rhombicus, and, like the opal, it belongs to the order Hyalina. The primary form of topaz in crystallography is a right rhombic prism. Its cleavage is parallel to its basal plane, almost perfect, and it cleaves so easily that a cut topaz, if dropped, might be easily cracked or broken. The crystallisation of topaz is imperfect; structure, columnar; lustre, vitreous; streak, white. Topaz is either transparent or translucent; the colours of topaz including wine, amber, honey, and straw-yellow, pale blue to pale green of many shades, greyish, reddish, and white. Rolled pebbles of limpid colourless topaz are called by Brazilians "pingas d'agoa," and by the French, "gouttes d'eau," both meaning drops of water. The coloured varieties show marked pleochroism. The fracture of this mineral is conchoidal and uneven.

True topaz is a silicate of alumina, containing hydroxl and fluorine; hardness, 8; specific gravity, 3.4 to 3.6. Being three and one half times as heavy as water, topaz can be readily distinguished from other stones resembling it by those accustomed to handling them. Topaz cannot be fused on charcoal before the blowpipe, but it is partially decomposed by sulphuric acid. Its hardness enables it to take a high polish, and the colourless variety has been cut in brilliant or rose form so as to resemble the diamond, for which it might readily pass in day-light. However, it is but weakly doubly refractive and dispersive, and its comparative softness makes its distinction from the diamond a simple matter. Although infusible, when sufficiently heated, the faces of crystallisation of topaz become covered with small blisters which crack as soon as formed; and with borax it slowly forms a clear glass. Some varieties assume a wine yellow or pink tinge when heated. The rose-pink topaz sometimes appearing mounted in jewelry, is not natural; the delicate tint of this gem with an artificial complexion results from a simple process called "pinking," applied to yellow or brown kinds. A topaz selected to be "pinked" is packed in magnesia, asbestos, or lime, and carefully and gradually heated to a low red heat; the stone then being slowly cooled. If the temperature attained has not been sufficiently high, the desired rose-petal tint is not obtained and a salmon tint appears; if the temperature rises too high, or is too long continued, the colour completely disappears. Pulverised topaz changes to green the blue solution of violets. Topaz generally becomes electric by heat, and if both terminations of the subject specimen are perfect, polarity will be developed; transparent varieties are susceptible to electrical excitation by friction.

Several minerals are commonly called topaz; yellow sapphire is called "Oriental topaz"; and varieties of quartz are called "Saxon," "Scotch," "Spanish," "Smoky," and "False" topaz. The hardness, weight, and power of developing frictional electricity, possessed by the true topaz, enable investigators to distinguish real topaz from these nominal varieties.

Topaz commonly occurs in gneiss or granite, associated with tourmaline, mica, or beryl, and occasionally with apatite, fluor-spar, and tin. The purest variety of topaz, perfectly colourless and pellucid, is not uncommon; as crystals it is found in Miask, in the Ural Mountains, Siberia, and, abundantly, as water-worn pebbles, in the river and creek beds of Diamantina and Minas Novas in the state of Minas Geraes, Brazil. Mineralogists regard the "Braganza," a gem claimed to be a diamond, included in the crown jewels of Portugal, and weighing 1680 carats, as one of these pebbles; probably one of the finest ever found. A sobriquet for these clear colourless topazes is "slave's diamonds." Blue topaz from Brazil is sometimes termed "Brazilian sapphire." A fine saffron-yellow variety, called "Indian topaz," occurs infrequently in Ceylon, and rarely, in Brazil; the golden yellow tinted variety from Brazil is the kind distinguished in the jewelry trade as "Brazilian topaz." Schneckenstein, near Gottesberg, in the vicinity of Auerbach, Voigtland, Kingdom of Saxony, is said, by Dr. Max Bauer, to be the most important European locality producing topaz; it is there imbedded in a steep wall of rock, and occurs in small fragments of schists rich in tourmaline, cemented firmly into a hard mass by quartz and topaz. Brazil is the main source of topaz, and a review of the localities, association, and varieties of its established occurrence there would require an extensive space.