KINDS OP KOCK& 



437 



Occurs in the gold regions of North Carolina and Brazil, and diamonds 

 are supposed to be sometimes connected as to origin with this rock. 



3. Siliceous Slate. — Schistose, flinty, not distinctly granu- 

 lar in texture. Sometimes passes into mica slate or schist. 



4. Chert. — An impure flint or hornstone occurring in 

 beds or nodules in some stratified rocks. It often resem- 

 bles felsyte, but is infusible. Colors various. Sometimes 

 oolitic. Kinds containing iron oxide graduate into jasper 

 and clay ironstone ; and others, occurring as layers or no- 

 dules in limestone are whitish, owing to the limestone 

 material they contain. Chert sometimes contains cavities 

 which are lined with chalcedony or agate, or with quartz 

 crystals. 



5. Jasper rock. — A flinty siliceous rock, of dull red, yel- 

 low, *or green color, or some other dark shade, breaking with 

 a smooth surface like flint. It consists of quartz, with more 

 or less clay and iron oxide. The red contains the oxide in an 

 anhydrous state, the yellow in a hydrous ; on heating the 

 latter it turns red. 



6. Buhrstone. — A cellular siliceous rock, flinty in texture. 

 Found mostly in connection with Tertiary rocks, and 

 formed apparently from the action of siliceous solutions on 

 preexisting fossiliferous beds, the solutions removing the 

 fossils and leaving cavities. 



Buhrstone is the material preferred for millstones. The buhrstone 

 of the vicinity of Paris, France, has long been largely exported for 

 this purpose. Good buhrstone is obtained also from the Tertiary in 

 Greenville District, South Carolina, 100 miles up the Savannah River. 



7. Fioryte. (Siliceous Sinter, Pearl Sinter, Geyserite.) — 

 Opal-silica, in compact, porous, or concretionary forms, 

 often pearly in lustre ; made by deposition from hot sili- 

 ceous waters, as about geysers (Geyserite), or through 

 the decomposition of siliceous minerals, especially about 

 the f umaroles of volcanic regions. 



Geyserite is abundant in Yellowstone Park, and about the Iceland 

 geysers ; after long exposure it crumbles down and becomes changed 

 to ordinary silica, or quartz. 



2. MICA AND POTASH-FELDSPAR SERIES. 



1. Granite. — Consists of quartz, orthoclase, and mica, and 

 has no appearance of layers in the arrangement of the mica 

 or other ingredients. G. = 2'5--2'8. The quartz is usually 

 grayish-white or smoky, glassy, and without any appearance 



