548 



MINERALOGY. 



flryctogrtd- 



Agate- 

 Jasper. 



Float-stone, 

 or Spongi- 

 form quartz. 



Agate. 



Indivisible 

 Quartz. 



Quartzy or 



Siliceous 



sinter. 



Hyalite. 



Cpal. 



Uses. When it occurs in sufficiently large masses, 



it is cut into various ornamental articles, as vases, snuff- 

 boxes, ringstones, &c. 



Fijlh Kind AGATE-JASPER, Jameson. Agat-Jaspis, 



Werner. 



External Characters Colours white, yellow, and 

 red. Several colours generally occur together, and 

 these arc arranged either in clouded, flamed, or striped 

 delineations ; of these the striped are either disposed 

 in a circular manner, or fortification-wjse. Occurs 

 massive. Frequently occurs in distinct concretions, 

 which are either fortification-wise bent, or concentric 

 lamellar. Internally dull. Fracture small and flat con- 

 choidal, approaching to even. 



Geognostic Situation. Occurs principally in layers, 

 in agate-balls, in amygdaloid ; likewise in agate balls 

 and veins in porphyry. 



Geographic Situation. Occurs in the agates of the 

 middle district of Scotland, &c. 



FOURTEENTH SUBSPECIES. 



FLOAT-STONE, or SPONOIFORM QUARTZ, Jameson. 

 Schwimmstein, Werner. Quartz nectique, Hazy. 



External diameters. Colours white and grey. Oc- 

 curs in porous, massive, and tuberose forms. Inter- 

 nally dull. Fracture coarse earthy. Feebly translu- 

 cent on the edges. Soft, but its particles are as hard 

 as quartz. 



Geognostic and Geographic Situations. It occurs 

 incrusting flint, or in imbedded masses in a secondary 

 limestone, at St. Ouen, near Paris. 

 AGATE, Jameson. 



Agate is not, as some mineralogists maintain, a simple 

 mineral, but is composed of various Hinds of the 

 quartz family, intimately joined together, .and the 

 whole mass is so compact and hard that it receives a 

 high polish. Agate is principally composed of calce- 

 dony, with flint, hornstone, carnelian, jasper, cacho- 

 long, amethyst, and quartz. Of these minerals, some- 

 times only two, in other instances more than three oc- 

 cur in the same agate ; and these are either massive, 

 disseminated, or in layers. 



II. INDIVISIBLE or UNCLEAVABLE QUARTZ, Jameson. 

 Untheilbarer Quartz, Mo/is. 



This species contains eight subspecies, viz. 1. Quart- 

 zy Sinter, 2. Hyalite, 3. Opal, 4. Menilite, 5. Obsi- 

 dian, 6. Pitchstone, 7. Pearlstone, 8. Pumice. 

 FIRST SUBSPECIES. 



QUARTZY or SILICEOUS SINTER, or PEARL SINTER, 

 Jameson. Kieselsinter, Werner. 



This is the siliceous incrustation met with around 

 hot springs in Iceland, and other volcanic countries. 

 SECOND SUBSPECIES. 



HYALITE,' Jameson. Hyalith, Werner. 



External Characters. Colours white, grey, and 

 green. Generally reniform, botryoidal, and sometimes 

 stalactitic, and in crusts. Internally shining and splen- 

 dent ; and lustre vitreous, slightly inclining to resin- 

 ous. Fracture conchoidal. Translucent, approaching 

 to semitransparent. 



Geognoslic and Geographic Situations. It has been 

 hitherto found principally near Frankfort on the 

 Mayne, where it occurs in fissures in vesicular basalt 

 and basaltic greenstone. 



THIRD SUBSPECIES. 



OPAL, Jameson. Opal, Werner. 



This subspecies is divided into seven kinds, viz. 

 Precious Opal, Common Opal, Fire Opal, Mother-of- 

 Pearl Opal or Cacholong, Semi-Opal, Jasper-Opal, 

 and Wood-Opal. 



First Kind PRECIOUS OPAL, Jameson. Edler Opal, 

 Werner. 



External Characters. Most common colour milk- 

 white, which at the same time displays a fine play of 

 beautiful colours. Occurs massive and disseminated. 

 Internally splendent, and vitreous. Fracture con- 

 choidal. Brittle. Uncommonly easily frangible. 

 Const. Parts. Silica, . . 90 



Water, . . 10 100 



Opal of Czscherwenitza, according to Klaprvth. 



Geognoslic and Geographic Situations. It occurs in 

 small veins in clay-porphyry, generally accompanied 

 with semi-opal ; in Hungary, and some other coun- 

 tries. 



Uses. Few gems are more beautiful than the opal, 

 The elegant play of the richest, purest, and most beau- 

 tiful colours, have procured for it a high rank among 

 the precious stones. It is worked into ringstones, 

 necklaces, ear-drops, and other ornaments. 



Second Kind. COMMON OPAL, Jameson. Gemeiner 

 Opal, Werner. 



External Characters. Colours white, grey, yellow, 

 red, and green. Occurs massive and disseminated. 

 Internally splendent, passing into shining j and vitre- 

 ous. Fracture conchoidal. Most commonly semi- 

 transparent. Of Telkobanya. 

 Const. Parts. Silica, . . 93.50 

 Oxide of iron, . 1.0 

 Water, . . 5.099.50 



Geognoslic and Geographic Situations. It occurs in 

 veins, along with precious opal, in clay-porphyry, in 

 Hungary and other countries. 



Third Kind FIRE OPAL, Jameson. FeurOpal,.K</r.rt. 



External Characters Principal colour hyacinth-red, 

 which passes through honey-yellow into wine-yellow ; 

 and upon lighter places shews a carmine-red and ap- 

 ple-green iridescence. In its interior, dendritic deli- 

 neations are sometimes to be observed. Internally 

 splendent, and lustre vitreous. Occurs in lamellar 

 distinct concretions. Fracture conchoidal. Complete- 

 ly transparent. 



Geognostic and Geographic Situations It has hither- 

 to been found only in America, at Zimapan in Mexico, 

 where it was first observed by Sonnenschmid and 

 Humboldt, imbedded in porphyry. 



Fourth Kind. MOTHER-OF-PEARL OPAL, or CACHO- 

 LONG, Jameson. Perlmutter Opal, Karslen. 



External Characters. Colour milk-white, and some- 

 times dendritic. Occurs massive and disseminated. 

 Externally dull; internally alternates from dull to 

 glistening and shining, and pearly. Occurs in granu- 

 lar distinct concretions. Fracture flat conchoidal, but 

 becomesearthy on the action of the atmosphere. Opaque. 



Geognoslic and Geographic Situations. It occurs, 

 along with calcedony, in trap rocks in the island of 

 Iceland ; in the Faroe islands ; also in Greenland ; and 

 in Bucharia. 



Fifth Kind. SEMI-OPAL, Jameson. Halb-Opal, Wer. 



External Characters Most common colours white, 



grey, and brown. Occurs not only massive and disse- 

 minated, but also tuberose, small reniform, small bo- 

 tryoidal, and stalactitic. Externally glistening; inter- 

 nally, generally glistening. Fracture conchoidal. 

 More or less translucent, and sometimes passes to 

 translucent on the edges. 



Geognostic and Geographic Situations. It occurs in 

 porphyry and amygdaloid, in Scotland, Iceland, France, 

 Germany, &c. 



Sixth Kind JASPER-OPAL, or FERRUGINOUS OPAL, 



Jameson. Opal-Jaspis, Werner. 



Oryctogno- 



y- 



Precious 

 Opal. 



Common 

 Opal. 



Fire Opal. 



Mother-of 

 Pearl Opal 



Semi- Opal. 



Jasper- 

 Opal. 





