HOB, 



[ 218 ] 



HOE 



composed of alumina, water, and 

 an acid to which Klaproth gave 

 the name of mellitic acid : the 

 latter constitutes 46 per cent, of 

 the whole. It differs from amber 

 in its weak electricity, double re- 

 fraction, and chemical character. 

 HO'ENBLENDE. The amphibole of 

 Haiiy. A mineral of a black or 

 dark green colour, often inter- 

 mixed : heavier than either quartz 

 or felspar, but less hard, its specific 

 gravity being between 3-15 to 3 -38. 

 It enters largely into the composi- 

 tion, and forms a constituent part 

 of several of the trap rocks, and 

 appears to connect the primary 

 with the volcanic. "When breathed 

 on, it yields a peculiarly bitter 

 smell. Before the blow-pipe it 

 melts easily into a black or grayish- 

 black, glass. There are many va- 

 rieties of hornblende, known as ear- 

 inthine, tremolite, actynolite, cala- 

 mite, amianthus, &c. &c. The 

 constituents of hornblende are, sil- 

 ica 45 '60, magnesia 18-50, lime 

 14, alumina 1-18, protoxide of 

 iron 7 1 50, fluoric acid 1'50. Mas- 

 sive hornblende is generally coarse- 

 ly granular and lamellar; when 

 intermixed with felspar in large 

 lamellar grains, it forms sienite. 

 This very common mineral may, 

 generally, be easily recognised. 

 Though sometimes in regular and 

 distinct crystals, it is more com- 

 monly the result of a confused 

 crystallization, and appears in mas- 

 ses composed of Iamina3, acicular 

 crystals, or fibres variously aggrega- 

 ted. Though inferior to schorl in 

 hardness, hornblende usually will 

 scratch glass, and, though with 

 difficulty, will yield sparks with 

 steel. Its laminated structure, its 

 inferior hardness, and its inability 

 of becoming electric by heat, dis- 

 tinguish it from schorl. It is less 

 hard and more easily fusible than 

 augite. It differs from epidote in 

 hardness, and the results of fusion. 



Its powder is not soft to the touch 

 like that of asbestus. 

 So' BE BLENDE SCHIST. One of the 

 metamorphic rocks, composed prin- 

 cipally of hornblende, with an un- 

 certain proportion of felspar, and 

 sometimes grains of quartz : its 

 colour is usually black. Dr. 

 M'Culloch observes, " hornblende 

 schist may at first have been mere 

 clay, for clay or shale is found 

 changed by trap into Lydian stone, 

 a substance differing from horn- 

 blende schist almost solely in its 

 compactness and in the uniformity 

 of its texture. Argillaceous schist, 

 when in contact with granite, is 

 sometimes converted into horn- 

 blende schist, the schist becoming 

 first siliceous, and, at the contact, 

 hornblende schist." 

 HOENE'EA. The name given by 

 Lamouroux to a genus of fossil 

 corals. One species, found in the 

 "Wenlock limestone, has been named 

 by Mr. Lonsdale, H. crassa, and is 

 by that gentleman thus described, 

 "Branches short, thick, flat, dicho- 

 tomosed; opening of the cells large, 

 elevated, and irregularly disposed 

 on one side ; opposite side striated ; 

 internal structure not ascertained. " 

 H'OENSTONE. The silex corne of 

 Brongniart; the quartz agathe 

 grossier of Haiiy; Hornstein of 

 Werner. Prof. Jameson divides 

 Hornstone into three sub-species, 

 namely, Splintery Hornstone, Con- 

 choidal Hornstone, and Woodstone. 

 A siliceous mineral ; a sub-species 

 of quartz. It has usually a dull 

 and splintery fracture, but some 

 times it is conchoidal. In appear- 

 ance it closely resembles compact 

 felspar, but it differs from felspar 

 in being infusible without the addi- 

 tion of an alkali ; it occurs massive, 

 and in extraneous external shapes; 

 lustre dull or glimmering, opaque 

 or translucent on the edges ; some- 

 times the whole mass, if thin, has 

 the strong translucency of certain 



