Oxide of Tin, in Crystals with 8-sided Pyramids
- Etain oxydé opposite. Haüy, v. 4. 141.
This is a rare modification. It is an incomplete 8-sided pyramid placed upon a 4-sided prism, at an angle of 155° according to Romé de l’Isle, and off 158° 45′ 27″ according to Haüy.
This pyramid is always terminated by another 4-sided one parallel to the octaëdron. They either stand on the gangue upright, with one end only finished pyramidally, as appears from the middle figure on the right hand, which is a large and curious detached crystal: being broken at the top, it gives an indication of a point, but on examination we find it cased on an octaëdron, which probably it once covered regularly; or they lie on their sides and are pointed at both ends: see the left hand figure. They are seldom large. The gangue is as usual to tin crystals, viz. rock crystal, chrlorite, and chlorite schist. or killas of the Cornish minders. The geometrical outline on the left hand shows the commencement of the 8-sided pyramid on the edge of the prism. There are many varieties of this modification on this specimen, and sometimes two of them meet base to base, and form a mackle: see the bottom figure.