298 POTTER'S ORE. 

 Analysis, from Sweden, by Thomson : 

 Silica ..... 49-01 

 Magnesia . . . .30-20 

 Alumina .... G'08 

 Protoxide of iron . . .11-40 

 Water 4-20 



100-89 



Localities. — British. Polyphant, near 

 Launceston, CornAvall. Loch Fyne, Argyle- 

 shire. Near Havre Gosslin, in Sark, Avhere 

 it is made into vessels for domestic use. — 

 Foreign. Norway. Sw-eden. Finland. Green- 

 land. Chiavenna, in the Valteline. Como, 

 in Lombardy. {^Pierre de Come.) The Val- 

 lais and Grisons. Wald, in Styria. Corsica. 

 Upper E^vpt. (See Pierre de BarajM.) 



Brit. Mus., Case 32. 



Potstone, from its infusibility, tenacity, 

 and softness, which admits of its being 

 turned in the lathe, has been used from 

 veiy early times for culinary vessels, and 

 a variety of other purposes. Vessels made 

 from Potstone are called in Italy and the 

 Grisons lavezzi, and possess the advantages 

 of heating quickly, and of not communi- 

 cating any taste to the substances cooked 

 in them. In Italy, -where it is called 

 ''pierre a pot,^' it is an object of considerable 

 trade. That from Como is brownish-black, 

 hard, and quite opaque, and withstands the 

 action of fire. It is also quarried at . Val 

 Sesia, near the village of Allagne, not far 

 from Monte Rosa. Another kind, found at 

 Queiras, near Brian^on, of an iron-grey 

 colour, possesses similar quahties. 



The Corsican Potstone is far superior to 

 that from Germany, and its manufacture 

 into a variety of ornaments and works of 

 art affords employment to many persons 

 in France, by whom it is made into candle- 

 sticks, taper-stands, snuff-boxes, &c. It 

 polishes with difficulty, but acquii'es con- 

 siderable translucency when cut thin. 



Potstone is but little employed in jew- 

 elry, but it is sometimes made into pretty 

 breloques, although it will not take a high 

 degree of polish. 



" Potstone *, by calcination white, acquires 

 Its name by turning on the lathe to most 

 Domestic uses." 



Potter's Ore. An old miner's name for 

 largely foliated pure Galena, or sulphide of 

 lead. In some countries such ores are styled 

 blue ores. 



Poudre d'Or or d'Argent. Names 

 given to the pounded Mica used on the 



* Wei-neria, or Short Characters of Earths, by 

 Terrffi Filius, page 28. 



PRECIOUS OPAL. 

 continent, instead of sand, for drying writ- 

 ing. 



PouNxA. See Borax. 



PozzuoLANA. Volcanic ashes from Ve- 

 suvius, -which, -when mixed with lime, form 

 a cement of the same name. 



Prase (from ^reaa-ov, a leek), a dark leek 

 green variety of vitreous Quartz, the colour 

 of which is caused by an admixture of Am- 

 phibole. 



Localities. The iron mines of Breitenbrunn, 

 near Schwartzenberg, in Saxony. The 

 Harz. The Cedar Mountain, S. Africa, in 

 fine crystals. 



Brit. Mus., Case 23. 



Praseolite, Erdmann. An altered form 

 of lolite, occurring in rounded rhombic 

 prisms Avith four, six, eight or twelve sides, 

 having a basal cleavage and a lamellar 

 structure. Colour green. Opaque or sub- 

 translucent. Lustre greasy. Fracture flat- 

 conchoidal or splintery. H. 8'5- S.G. 2-754. 



Comp. IoIite + 3H (Rammelsberg), or Si 



(Mg + Al) + H (Mg,Fe, Mn) Si + 2 AlSi + H. 

 (Erdmann.) 



Analysis, from Brakke, by Erdmann : 



Silica 40-94 



Alumina .... 28-79 

 Protoxide of iron . . . 6-96 

 Magnesia .... 13-73 

 Protoxide of manganese . 0-32 

 Oxides of lead, copper, lime, 



cobalt .... 0-50 

 Titanic acid . . . 0-40 

 Water 7-38 



99-02 



BB fuses with difficulty at the edges to 

 a bluish-green glass. 



Locality. Brakke, near Brevig, in Nor- 

 way; in quartz-veins traversing gneiss. 



Name. From jt^^'tov, a leek, and ^I'Soi, 

 stone, in allusion to its leek-green colour. 



Brit. Mus., Case 3-2. 



Prasochrome, Landerer. Carbonate of 

 lime coloured by oxide of chrome, resulting 

 from the alteration of Chromic Iron, and 

 forming a dull green incrustation, on the 

 Island Scyro, in the Grecian Archipelago. 



Precious Beryll, Jameson. See Beryl 

 and Aquamarine. 



Precious Garnet. See Pyrope, also 

 Garnet. 



M.P.G. Horse-shoe Case, Nos. 890 to 898. 



Precious Opal. Includes those varie- 

 ties of Opal which exhibit a rich play of 

 prismatic colours : it is always cut with a 



