EPISTILBIT. 



four groups: 1. Lime-and-iron-Epidote ; 

 Arendalite ; Bucklandite ; Pistacite or Epi- 



EPSOMITE. 



129 



Fig. 176. 



Fig. 177. 



dote proper; Puschkinite. 2.. Lime Epi- 

 dote; Zoisite. 3. Manganesian Lpidote. 

 4. Cerium Epidote; AUanite; Ihulite, 

 Withamite. . 



These are described under their various 

 names. ^ . , , 



The general formula for Epidote, accord- 

 ing to Hermann, is (K^ ft) Si + « R H, as 

 translated by Dana. 



J55 fuses more or less easily, according to 

 the amonnt of iron or manganese. In 

 powder, after fusion or ignition dissolves in 

 muriatic acid, and forms a jelly of silica. 



Name. From Wt'toa-i;, increase; because 

 the base of the primary form undergoes an 

 increase in some of the secondary forms. 



Epidote occurs in granite and other 

 igneous rocks, and in various crystalline 

 slates in attached crystals, generally 

 grouped in druses, and in granular or 

 columnar masses. Colour generally green, 

 yellow and grey ; sometimes red and black. 

 Semi-transparent to transparent at the 

 edges. Lustre vitreous ; pearly on cleavage 

 planes. Streak grey; except in the man- 

 ganese variety from St. Marcel, which is red. 

 Brittle. Fracture uneven— splintery. H. 6 

 to 7. S.G. 3 to 3-5. 



Brit. Mus., Case 35. 



M.P.G, Horse-shoe Case, Nos. 1030 to 

 1032! 



Epistilbit, Rose ; Epistilbite, Phillips. 

 Ehombic: primary form a right rhombic 

 prism. Commonly occurs in macled crystals. 

 Colour white, bluish or yellowish-white; 

 varying from transparent to translucent 

 only at the edges. Lustre vitreous : on the 

 faces of cleavage pearlv. Fracture uneven. 

 H. 3-5 to 4. S.G. 2-249 to 2-363. 



Fig. 178. 



Fig. 179. 



one atom less of water ; or, (Ca, Na) Si3 + 



AISP + 5H = silica 59-3, alumina 16-8, 

 lime9-2, water 14-7 = 100-0. 



Analysis, from Berufiord, by Rose : 

 Silica ..... 58-59 



Alumina 

 Lime . 

 Soda . 

 Water . 



17-52 



7-56 



1-78 



14-48 



99-93 



Camp. The same as that of Stilbite, with 



When heated swells up strongly and 

 evolves water. 



BB alone, becomes white, intumesces and 

 yields a highly blistered enamelj which does 

 not run into a globule : with soda fuses to 

 a transparent blistered glass. 



Dissolves in concentrated muriatic acid, 

 with separation of silica in the form of a 

 granular powder. 



Localities. The Isle of Skye, in small 

 flesh-coloured crystals, in cavities in amyg- 

 daloid. In large distinct crystals in the trap 

 rocks of Iceland (Berufiord), and the Faro 

 Islands. Poonah in India. Bergen Hill, 

 New Jersey, &c. 



Brit. Mus., Case 38. 



Epsomite, Beudant; Upsom Salt, 

 Kirwan. Rhombic: primary form a rhom- 

 bic prism of 90° 30' and 89° 30'. Occurs in 

 botryoidal masses, and capillary efflores- 

 cences. Colour and streak greyish -white. 

 Transparent to translucent. 'Taste bitter 

 and saline. Very brittle. H. 2-25. S.G. 

 1-751. 



Comp. When pure, Mg S + 7H = mag- 

 nesia 16-26, sulphuric acid 32 52, water 

 51-22 = 100-00. 



BB dissolves very easily by the assist- 

 ance of its water of crystallization, but is 

 difficultly fusible. Soluble in less than 

 double its weight of cold water. 



Localities. British. — Is a common in- 

 gredient in many mineral waters, as in 

 those of Epsom, in Surrey ; and appears as 

 an efflorescence on the surface of certain 

 rocks, as at the old coal-wastes and alum 

 mines at Hurlet near Paisley, where it forms 

 white capillary crystals. Foreign. — i:\xe 

 quicksilver mines of Idria in Carniola. The 

 gypsum quarries of Montmartre, near Paris. 

 Aragon and Catalonia, in Spain. The mines 

 at Clausthal in the Harz. 1 he Cordillera of 

 St. Juan, in Chili. Mammoth Cave of 

 Kentucky, adhering to the roof in loose 

 masses like snowballs. 



Brit. Mus., Case 55. 



