MINERALOGY, 



545 



IOLITI. 



Pmroitu- 

 Kbomboi- 



Jil 



Juitli. 



Rhombol- 

 dal quarti. 



Amet'iril. 



with rock-crystal and topaz, in the upper parts of Aber- 

 deenshire. In Ireland, imbedded in granite, near 

 Lough Bray, in the county' of Wicklow, and near 

 Cronebane in the same county. 



r{ ._When pure, it is cut into ring-stones, seal- 

 stones, brooches, intaglios, and necklaces, but is not so 

 highly valued as emerald. 



GENUS VIIIOLITE. 



Cleavage rhomboidal. Hardness=7.0 7- ... Sp. gr. = 

 2.5. 2.6. 



1. PRISMATO-RHOMBOIDAL IOLITE, Jameson.- lolith 



and Peliom, Werner. 



Rhomboid unknown. Cleavage in the direction of the 

 lateral planes of the regular six-sided prism. 



External Characters Colour intermediate between 

 violet-blue and blackish-blue. When viewed in the di- 

 rection of the axis of the crystals, the colour is dark 

 indigo-blue ; but perpendicular to the axis of the cry- 

 stals, pale brownish-yellow. Occurs massive, dissemi- 

 nated, and rar-ly crvtalli/ed in six-sided prisms. 



Interns!'- and the lustre vitreous. Fracture 



small-grained uneven, and sometimes conchoidal. Trans- 

 lucent in the direction of the axis of the crystal, and 

 irent at right angles to it. Refracts double. 

 it. Parts. Silica, . 43.6 



Alumina, 



Magnesia, . 9.7 



Potash? . 1.0 



Oxide of Iron, . 4.5 



: manganese, a trace -99.5 



Leopold Gmelin. 



,'nustic and Geographic Situation*. It is found 

 rijarvi, near Abo in Finland; at Hodenmais in 

 Bavaria ; in the country of Salzburg ; and in other parts 

 of Europe and America. 



/ a-. It is cut, polished, and worn as a gem. 



GENUS VII. a. QUARTZ. 



Rhomboidal. Cleavage rhomboidal, not axifrangiblc. 

 Hardness = 3.5- -|>. Or. = !.< 2.7. 



1. RHOMBOIDAL QUARTZ, Jameson. (Quartz, Wer- 

 ner. Rhoinbni :, Mohs. 



Rhomboidal. Rhomboid = 7(1 V. Cleavage in the 

 direction of the alternate planes of the double six-sided 

 :iid in the direction of the lateral planes of 

 led pri-m. Hardness = 7.0. Sp. gr. = 2.5 

 This species contains fourteen subspecies, viz. 1 . Ame. 

 -tal, 3. Milk Quartz, 4. Common 

 Prase, 6. Cats-eye, 7. Iron Flint, H. Horn- 

 stone, 9. Flinty Slate, 10. Flint, II. ( alcedony, 12. He- 

 liotrope, IS. Jasper, 14. Floatstone, Agate. 



FIRST SUBSPECIES. 

 AMETHYST. 



External Character*. Colour violet-blue. Occurs 

 massive, and in prismatic and lamellar concret 

 Most frequent crystallization is the acute six-sided 

 t form is the six-sided prism 



with a six planed acumination. Alternates from 



translucent to transparent. Internally splendent, or 



.'. and lustre vitreous. Fracture conchoidal. 



i 'nation. It occurs in agate-balls in 

 1, green-stone, and porphyry, and in veins 



>ndary rocks. 



Geogrmpkic Situation. In veins and drusy cavities in 

 secondary greenstone and amygdaloid, in many parts 

 of Scotland. Near Cork in Ireland. In many places 

 continents of Europe, Asia, Africa, and America. 

 ( ./. The mort highly valued amethysts are those 

 bronght t. :itinent of India, and the Island of 



Ceylon. The next in esteem are the Brazilian. When 

 th colour i good, it is cut and polished, and is consi- 

 dered gem of considerable beauty. 



OL. XIT. PART II 



SECOND SUBSPECIES. Oryctogno- 



ROCK or MOUNTAIN CRYSTAL, Jameson Bergcrys- .-_**[ m _ l . 

 tal, Werner. Hock or 



External Characters. Colours white, brown, yellow, Mountain 

 and red. Generally occurs in crystals, which are usual- crystal, 

 ly six-sided prisms acuminated, with six planes set 

 on the lateral planes. Externally the crystals are 

 generally splendent or shining. Internally, splendent 

 and vitreous. Fracture almost always perfect conchoi- 

 dal. Generally transparent. 



Chemical Characters. It is completely infusible be- 

 fore the blowpipe. 



Constituent Parts. Silica, 99f 



Trace of ferruginous 



Alumina. 100 



Bucholz, Gehlen's Journ. 1808, p. 150. 



Geognotlic Situation. Although rock-crystal occurs 

 more frequently, and in more numerous geognostic 

 relations than amethyst, yet it is not the most common 

 subspecies of quartz. It appears most frequently, and 

 in the largest and most transparent crystals, in primi- 

 tive rocks, where it occurs in beds, veins, and large 

 drusy cavities. 



Geographic' Situation. Crystals of great size and 

 beauty are found in different parts of Scotland ; the 

 rock-crystals of the Island of A rran, which occur in 

 drusy cavities in granite, are well known ; but the 

 largest and most valuable are found in the district 

 of Cairngorm, in the upper part of Abenlcenshire. 

 where they occur in granite, or in alluvial soil, along 

 with beryl and topaz. On the Continent of Europe it 

 is very widely, and often abundantly distributed, and 

 the same is the case in Asia and America. 



I'set. Rock-crystal is cut and polished as an inferi- 

 or kind of gem or ornamental stone. 

 THIRD SUBSPECIES. 



ROSE or MILK QUARTZ, Jameson Milch Quartz. Rose or 



Werner. Mflk 



External Characteri Colours rose-red and milk- Q""'*- 

 white. Occurs only massive. Internally shining, 

 sometimes passing to splendent, and vitreous, inclining 

 to resinous. Fracture more or less perfect conchoidal. 

 More or less translucent. The other characters are the 

 same as those of rock-crystal. 



Geognostic Situation. It occurs in masses, included 

 in beds of quartz subordinate to granite and gneiss, and 

 in veins of manganese in granite. 



Geographic Situation. It occurs in primitive rocks 

 in Scotland, Germany, and in Europe, and in various 

 districts in Asia and America. 



Utet It is employed in jewellery, and the larger 

 masses are cut into vases. 



FOURTH SUBSPECIES. 



COMMON QUARTZ, Jameson. Gemeiner Quartz, 

 Werner. 



External Character*. Colours white, grey, yellow, 

 brown, red, green, blue, and black. Occurs massive, 

 disseminated, in plates, stalactitic, reniform, botryoidal, 

 globular, specular, corroded, vesicular, ramose, amor- 

 phous, cellular, and with impressions. Internally 

 shining, which sometimes borders on glistening, and 

 sometimes approaches to glimmering, and is vitreous. 

 Fracture coarse splintery, and conchoidal. Generally 

 translucent The other characters the same as those of 

 rock-crystal. 



Geognostic .Situation. It is one of the most abun- 

 dant minerals in nature, and appears in many different 

 geognostic situations. It occurs in primitive, transition, 

 secondary, alluvial and volcanic rocks, and either as a 

 constituent part of these rocks, or associated with thorn 

 in the form of beds and veins. 



t* 



