MINERALOGY. 



Wood-ftone, Qiiart agathe xyloule, Haiiy, is gencrally 

 various fliades of grey, frequently ftriped or clouded. It 

 occurs rounded, and in the fliape of the trunks, branches, or 

 roots of trees ; it is generally tranflucent at the edges, with 

 little or no lullre. The crols fracture is imperfeftly con- 

 choidal, the longitudinal fplintery and fibrous. Wood-ftone 

 is properly wood fihcified, in which the greater part of 

 the vegetable matter has difappeared, and filiceous matter 

 has occupied the place, prcferving the form and texture of 

 wood. Some wood is petrified with opal, forming wood 

 opal ; and fometimes the mineral matter of petrified wood is 

 quartz, or calcareous earth. 



Hornblende, Amphihoh, Haiiy. The defcription of 

 this mineral, fo important in geology, was omitted in the 

 proper place, and is given here. Hornblende may be 

 divided into common hornblende, bafaltic hornblende, and 

 hornblende (late. Haiiy, under the term amphibole, claffes 

 aetinolite with hornblende. (See Actinolite. ) Horn- 

 blende generally occurs of various (hades of dark green 

 pafTnig into black ; fometimes common hornblende occurs of 

 various (hades of brown. Hornblende has a lamellar ftrvic- 

 ture longitudinally, with a two-fold oblique angular clea- 

 vage, pai-allel to the planes of a rhomboidal prifm, the alter- 

 nate angles of which are i 24^° and 565°. This is the form 

 of the prim.itive cryftal, and diftingui(hes it from epidote, 

 which cleaves at an angle of 1 14-|- and d^ii, and augit or 

 pyroxene, which cleaves at an angle of 92" and 88°. The 

 crofs frafture of hornblende is coarfe-grained, uneven ; it 

 melts eafily before the blow-pipe into a greyidi-black co- 

 loured glafs. Thefe charafters, together with the cleavage, 

 ferve to diftinguifh hornblende from augit or epidote ; its 

 inferior hardneis diftinguilhes it from fchorl. 



Common Hornblende occurs both maffive, di(reminated, 

 and cryftallized ; the cryltals are oblique four-fided prifms, 

 aggregated or long fiattilh prifms, interfetting each other, 

 or confufedly radiated. The il:ructure is lamellai- or bladed. 

 The cryftals are long and deeply ftreaked longitudinally. 

 The lullre is (hining and pearly. The black-coloured 

 varieties are opaque ; the green generally tranducent at the 

 edges. It yields pretty eafily to the knife, leaving a greenilh- 

 grey ftreak. It is very tough, and becomes indented by 

 the ftroke of a hammer. The fpecific gravity is from 3.20 

 to 3.28. According to Klaproth, the conftituent parts 

 are, 



Silex .... 



Alumine - - - . 



Lime - - . . 



Magnefia - - . . 



Oxyd of iron - . . 



Ferruginous manganefe 



Water - . . . 



A trace of pota{h 



98.25 



This mineral occurs forming beds in mountains, or 

 is diffeminated, as a conftituent part of many compound 

 rocks. It occurs occafionally in granite, gneifs, mica-flate, 

 and flate, and is an eflential part of fienite and green-ilone. 

 It forms a conilituent part of many bafaltic and volcanic 

 rocks, but has frequently been confounded with augit. 

 (See Volcanic Producls.) Hornblende occurs abun- 

 dantly in various parts of Scotland and in England, parti- 

 cularly at the Malvern-hills in Worcellerfliire, and at Char- 

 wood foreft in Leicefterfliire, and in Devonfhire, Cornwall, 

 and Cumberland. 



Bafaltic Hornblende, Amphibole fchorlique hafaltique, Fr. is 



di(lingui(hed from common hornblende by its velvet-black 

 colour, and more perfeft cryftallization. It occurs cryf- 

 tallized in unequiangular fix-lided prifms, terminated at 

 each extremely by a trihedr:J pyramid, with rhombic faces. 

 It is lometimes terminated diflimilarly at each extremity, and 

 fometimes acuminated by four or more planes. The angles 

 of the cleavage have been already defcribed. Bafaltic horn- 

 blende has a fplendent vitreous lufire. The frafture is fine- 

 grained, uneven, and ghftening. It is black, opaque, and 

 (cratches glafs. It is more frangible than common horn- 

 blende, and melts with greater difficulty. The fpecific 

 gravity is from 3.15 to 3.19. According to Klaproth, the 

 conftituent parts are, 



Silex 



Alumine - 

 Lime 



Magnefia - 

 Oxyd of iron 

 Water 



47.00 



26.00 



8.00 



2.00 



15.00 



0.50 



98.50 



It occurs imbedded in bafalt, as at Arthur's feat, near 

 Edinburgh, and in various parts of Scotland. It is fre- 

 quently found in lava, particularly in the lava of Vefuvius. 

 It was formerly confounded with fchorl, until Werner 

 pointed out its charafters. 



Hornllende-Slate occurs in beds in granite, gneifs, and 

 mica-flate ; in the latter rocks, it is often much intermixed 

 with mica, and fometimes contains garnets, as is the cafe 

 near Tyndrum in Perthfliire. Its colour is greenirti-black. 

 It has in the mafs a flaty ftrufture, and is internally laminar 

 or fibrous, and has a gliftening or velvet-hke luftre. No 

 very well charafterifed beds of hornblende-fiate occur in 

 England. 



Horn-Mercury, Mercure muriate, Haiiy. See Mer- 



CURY-OrfJ-. 



Horn-Silver, Argent muriate, Haiiy. See Silver- 

 Ores. 



Humite occurs at mount Somina near Naples, in a gra- 

 nular topaz rock, intermixed with brown and olive-green 

 mica and white Haiiyne. Its colour is reddi(h-brown ; it 

 occurs cryftallized in oclahedrons, which are always more 

 or lefs truncated and bevelled ; the planes are frequently 

 tranfverfely lireaked ; it has a fliining luftre, and is tranf- 

 parent ; it fcratches quartz with difiiculty. This mineral 

 was named humite in honour of fir Abraham Hume, by the 

 count de Bournon, who has given the preceding characters 

 of it in his Catalogue Mineralogique. 



Hyacinth, Zircon hyacinth. See Zircon. 



Hyalite, Midler glafs, Werner ; Quarz concretione, 

 Haiiy. (See Hyalite.) The fpecific gravity of this 

 mineral is given in the lalt edition of profeflbr Jamefon's 

 Mineralogy at 2.47, from Karften. Its conftituent parts are 

 given by Bucholz as under : 



Silex 



Water 



Trace of alumine 



Lofs 



92 

 6-33 



1.66 

 99.99 



Hydrate of Magnefahni a white colour with a grecnilh 

 tinge ; it occurs malftve, has a lamellar-bladed ftrudure, a 

 pearly luftre, and is more or lefs femitranfparent, but be- 

 ^ ' comes 



