SURVEY OF COLORADO AND NEW MEXICO. 107 



1. Smoky quartz and black quartz. — Elk Creek. 



2. Rock or Berg crystal. — Near " Dirtywomau's Eaucli," and in geodes 

 in various mines. 



3. Rose quartz. — Quartz Hill. 



4. Agate, (moss agate, &c.) — Middle Park, Arkansas River Park, &c. 



5. Amethyst. — Nevada City, Mill City, «&c. 



6. Aventurine. — Elk Creek. 



7. Heliotrope, (bloodstone.) — Middle Park. 



9. Carneliau. — South Park and Middle Park. 



10. Chalcedony. — South Park, Trout Creek Pass, &c. 



11. Chrysoprase. — Middle Park. 



12. Jasper. — South and Middle Parks. 



13. Onyx.— Middle Park, Grand River, &c. 



14. Sardonyx. — Golden City, Mount Yernon. 



Hornstone, flint, milk quartz, prase, catseye, firestone, and other 

 different varieties of silicic acid, are met with in the above localities, but 

 have no especial interest. 



Opal, (hydrated silicic acid.) — Idaho City, Golden City, Soutb Boul- 

 der, &c. 



Feldspar. — Very abundant in the mountains and as boulders and 

 pebbles thro\ighout the Territory. Associated with quartz in the granites, 

 gneisses, and i)ori3hyries of the gold-bearing mountains. 



a. Orthoclase (AI2O3 . 3Si03 -f KO.SiOa) is largely the predominant 

 feldspar in the rocks of Colorado. 



a 1. Pegmatolite. — Flesh-red, orthoclastic, abundant as pebbles, scat- 

 tered with quartz over the prairies for hundreds of miles. Forms red 

 granites and gneisses with quartz and mica, and red syenites with horn- 

 blen de. Very com mon . 



a 2. Adularia. — Forms a white porphyry w^hen associated with quartz 

 in many places along Fall River, and in many veins. Not common. 



a 3. Sanidin. — Fine crystals of hopper-shaped sanidiu from Quartz Hill. 



h. Plagioclastic feldspars. 



I) 1. Albite, (AI3O3 . aSiOs + NaO . SiOs.j— Trout Creek Pass. 



h 2. Oligoclase. — Arkansas River Park, &c. 



h 3. Labrador, (AI2O3 . SiOg + CaO . SiOa.)— In thebasalts and diabases 

 of the region about the Spanish Peaks, Trinidad, the upper part of San 

 Luis Park, and the Puutia Pass. 



Sornhlende, (silicate of lime, magnesia, and suboxide of iron). — In the 

 syenite in and around Idaho. 



Diorite. — Near Empire City and elsewhere. 



Garnet— South Park, twenty miles from Fairplay. Breckenridge. 



Mica, (KO . SiOs -f AI2O3 . Si03 + RO . SiOj.) 



1. Potash mica.— Light colored. Frequent in the gneisses of Gilpin 

 and other counties. 



2. Magnesian mica.— Dark colored. Frequent in the gneisses of South 

 Park, Trout Creek Pass, &g. 



Leucife, (AI2O3 . SiOs + KO . SiOs.)- In trachytic lava between the 

 Cuchara and the Apishpa. 



Chlorite. — In diabase, near Trinidad. 



Ampliihole, (augite).— In basalts, near Trinidad, and diabase near 

 Apishpa. 



Epidote, (CaO . Si03 + [AI2O3 + FczOs] SiOg.)— Trail Creek. 



Tourmaline. — Guy Hill. 



Calc spar, (CaO . C02.)— Very widely distributed. Idaho, &c., &c. 



Gypsum, (CaO . SO3 + HO.)— Interstratifled in the new red sandstone 



