Of the tin ore deposits of Mount Bischoff, Tasmania

From Baron von Groddeck, chief mining councillor of the Hartz mining districts, and director of the Royal Prussian academy of mines at Clausthal, Germany.
(Translated by Edgar Wolfhagen, M.B., Hobart, from the Special Imprint of the "Magazine of the Geological Society," 1886.) Attention was again drawn to the collection of specimens of minerals from Mount Bischoff, Tasmania, in the possession of the Royal Academy for Mineralogy in Clausthal. This collection has previously afforded me an opportunity for making a communication about a porphyritic topaz rock and about a peculiar topaz tourmaline deposit in the Tasmanian tin district.
It appears, therefore, as if in the tin district of Tasmania (as in the Schueckenstein in the south-west of Saxony) a transformation of the rocks with topaz had taken place during the formation of the tin deposits. This is a previously unknown geological process of the highest interest, since it introduces new views as to the origin of the tin deposits. This process is probably not so isolated as would at present appear. The discovery made by M. Schroeder is the more interesting, as many pseudo-morphoses from topaz to other minerals are known, but no change of another mineral into topaz. On the Schueckenstein the transformation with topaz occurs, according to M. Schroeder, by the topaz replacing both tourmaline and feldspar. Minute crystals of topaz protrude into the clear quartz in the form of needles, fibres, and bundles of fibres, or even lie, apparently isolated, in among the quartz. The topaz is to be distinguishd from the quartz by ordinary light, by its dull colouration, and very finely granular or radiating fibrillar structure.
It remains undecided, therefore, whether the Tasmanian tourmaline-quarzit slate has undergone a transformation into topaz, as is the case in that of Saxony.