Phosphate of Lead

The yellow phosphates of lead of Wanloch-head mines, Scotland, are found coating Galæna in the Bellan-grain vein, from 20 to 30 fathoms below the surface, but gradually disappear at greater depths. From this mine our specimens came by favour of G. Laing, Esq. They are found in other parts of Great Britain besides Scotland, as Wales, Cornwall, Ireland, &c. The purest phosphates seem to be of the brightest yellow, and the crystals are generally very small, being mostly hexaëdral columns and their modifications. The present is in very perfect hexaëdral columns, and its yellow varies in intensity, with a greenish and brownish cast. The crystals are soft, brittle, easily scraped with a knife, and the powder^* corresponds with the colour of the crystal. The crystals will easily scratch carbonate of lead. Fracture splintery and conchoidal. “Integrant molecule in irregular tetraëdron. Primitive form a bipyramidal dodecaëdron.”—Haüy. We find these at first, by exposure to the blowpipe, turn green; then they assume a pearly cream colour, and afterwards become irregularly fibrous. The heat being continued, these fibres united in a somewhat concentrating manner, forming various polygonal facets in an irregular sort of crystallization: see the left hand figure at the bottom. This substance is sometimes situated on an amorphous matrix of its own nature, or on quartz, ochraceous quartz, galæna, &c., as before observed.