Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/372



Bardiglione of a determinate Figure.

The crystalline state is that in which this substance most commonly occurs; but its forms are seldom determinate. The finest crystals, and the greatest variety, have been found in the mine of rock-salt at Hall in the Tyrol; which is also the place where it has been most commonly observed of a determinate crystalline figure. The crystals occur there in groups, either colourless, or of a pale red slightly inclining to violet. They are commonly pretty large, frequently flattened, and often of very little thickness. They intersect each other in different directions, and very often several are joined together so as to have the appearance of a single crystal: but in these cases their lines of separation are readily perceivable; and, as they adhere together but slightly, they are easily separated. Sea-salt is frequently found disseminated through these crystals; and in this case, the same salt very often also shews itself externally in small distinct masses, which are easily known by their inferior lustre and hardness. When the Abbé Poda first noticed these substances, it was the variety of Hall that came under his observation. The sea-salt, of which there are frequently considerable masses in it, led him to consider it as a mixture of this salt with gypsum. Its rectangular figure also contributed to this error, which made him give it the name of Muriacite.

In 1802, when Mr. Chenevix analysed this variety of bardiglione from Hall, at my request; the person employed in pulverizing it found some small needles of antimony included in the interior of one of the crystals, most of them adhering to small groups of crystals of quartz; and to prevent all dispute about it, he preserved a fragment of the crystal, to which one of these needles still adhered. This fact,