286 PICROTHOMSONITE. 



Comp. Hydrated silicate of magnesia, or 



Mg2 Si2 + H = silica 55-9, magnesia 36, 



water 8-1. 



Analysis, from Presnitz, by Magnus : 



Silica 64-89 



Alumina .... 0*79 

 Peroxide of iron . . , 1"40 

 Magnesia .... 33'3o 

 Protoxide of manganese . 0*42 

 Water . . . . . 7-30 



98-15 

 BB does not fuse, but increases in den- 

 sity, becomes black and afterwards white 

 and opaque. Dissolves in borax and mi- 

 crocosmic salt, in the latter case leaving a 

 skeleton of silica. Assumes a pale red 

 colour when ignited with a solution of 

 cobalt. 



Localities. In the iron mine of Engels- 

 berg, near Presnitz in Bohemia, in a bed in 

 gneiss, associated with Magnetic Iron Ore. 

 Greiner in Tyrol. Waldheim in Saxony, 

 I Name. 'From a-z^go?, bitter, and «V^r/, 

 smell; in allusion to the bitter argillaceous 

 odour it gives out when breathed on. 



PiCROTHOMSONiTE, A mineral resembling 

 Thomsonite in form, but differing from it 

 in having the soda replaced by magnesia. 

 Occurs in radiated masses with a laminated 

 structure. Colour white. Lustre pearly. 

 Transparent in thin fragments. Very fra- 

 gile. H. 5. S.G. 2-278 



Comp. (Ca, Mg)5 si + 2iSi AI + 4iH. 



Analysis : 



Silica 40-36 



Alumina .... 31-25 



Lime 10-99 



Magnesia . . . .6-26 

 Soda and potash . . .0-29 

 Water ..... 10-79 



99-94 



BB intumesces and fuses to a white 

 enamel. 



Dissolves in cold acid with the formation 

 of a jelly of silica. 



Locality. Tuscany, associated with Ca- 

 porcianite, in gabbro rosso. 



Name. From -rix^cn, hitter, and Thom- 

 sonite ; in allusion to the presence of mag- 

 nesia. 



Fig. 334. 



PIERRE CALCAIRE. 



PiCTiTE. A name under which Tur- 

 ner! te (^Fig. 334) has been occasionally 

 brought to this country. 



PiDDlNGTONiTE, Haidinger. A mineral 

 substance composing nearly the whole of a 

 large meteorite of a breccia-like aspect, 

 which fell at Shalka in the East Indies, 

 with the usual phenomena of light and de- 

 tonations, on the oOth of November 1850, 

 The Piddingtonite is of an ash-grey colour, 

 more or less fine-grained, very fragile, 

 (though of considerable hardness), more or 

 less translucent, of oil-like brightness, im- 

 perfectly cleavable in two directions inter- 

 secting at angles of about 80° and 100°, 

 and Avithout magnetic action. H. 6-5. 



Name. In honour of the late Mr. Pid- 

 dington. Curator of the Calcutta Museum 

 of Practical Geology. 



PiEDMONTiTE. A name for Manganesian 

 Epidote from Piedmont. 



Pierre aluminedse, Brochant. See 

 Alum-stone. 



Pierre A briquet, ") Names given in 



Pierre a feu, > France to ordi- 



PiERRE A fusil. J nary Chalk-flints, 

 and having reference to the purposes to 

 which they were applied before the intro- 

 duction of percussion locks to fire-arms, and 

 the invention of more ready ways of ob- 

 taining a light than by means of the old- 

 fashioned tinder-box. 



Pierre A Jesus. According to Beudant, 

 a name given to transparent lamellar va- 

 rieties of Gypsum (Selenite), in consequence 

 of their being sometimes used, when di- 

 vided into thin lamina, instead of glass, 

 for covering small images. 



Most likely, as suggested by Mr. War- 

 rington Smyth, the term is merely a cor- 

 ruption of the Italian Gesso, or Spanish 

 Yeso ; words themselves derived from yv^os, 

 the Greek name for Gypsum. 



Pierre A lancette, A name given to 

 green Jasper on account of its being used 

 for sharpening lancets in Java. It is, also, 

 found in France, in the Dept. of Isere, and 

 in Sicily. 



Pierre A magot. See Agalmatolite. 



Pierre A noyaux. See Coccolite. 



Pierre A platke, or Plaster-stone. See 

 Gypsum. 



Pierre A pot. See Potstone. 



Pierre calaminaire. See Calamine. 



Pierre calcaire d'Edelfors. See 



J^^DELFORSITE. 



Pierre calcaire puante, La Metherie. 

 See Stinkstonb. 



