422 Turner — Rocks and Minerals from California. 



Petrographic description of the diorite. — Megascopicall y the 

 diorite is a grayish-green medium-grained rock showing very 

 abundant short needle-iike prisms of a green mineral. Micro- 

 scopically the rock has a granolitic texture. It is composed of 

 amphibole > feldspar > quartz. The accessory minerals are 

 rutile in irregular brownish red grains, apatite in minute 

 prisms, occasional grains of magnetite and possibly a few zir- 

 cons. Epidote, chlorite and sericite are present as secondary 

 products. 



The most abundant constituent, the amphibole, is grayish- 

 green in color and occurs chiefly in the form of short needles 

 which show idiotnorphic outlines in sections transverse to the 

 prism. The amphibole is clearly embedded in the feldspar and 

 quartz and therefore earlier. The absorption is £>!£>#. t 

 is brownish-green, ft green and ft very light green. The 

 maximum value of the extinction angle t on a is 23° as deter- 

 mined by measurements on 55 needles. The feldspar in part 

 shows twinning on the albite law with rather low symmetrical 

 extinction angles on 010 in the few grains measured, suggest- 

 ing oligoclase or andesine. The feldspar is partly quite fresh 

 but some of it contains minute brightly polarizing fibers, prob- 

 ably sericite. The quartz is fresh and clear and like the feld- 

 spar, undoubtedly primary. The chlorite is supposed to be an 

 alteration product of the amphibole. It is green in color and 

 very noticeably pleochroic. The fibers are grouped in rosettes 

 showing olive-gray interference colors. For the purpose of 

 making a separation of the constituents of the rock 48 grams 

 of the powdered rock were passed through a wire sieve with 

 spaces lOOth of an inch in diameter. The fine dust and the 

 larger part of the light material (chiefly feldspar and quartz) 

 was washed off with water in a batea. The remainder was put 

 in a Thoulet solution of maximum specific gravity (about 3*18 ?) 

 only a small amount of the material being precipitated. This 

 was separated and found to weigh about 0'35 grams. A mag- 

 net was passed over this powder and a few grains of magnetite 

 extracted. This heavy powder as seen under the microscope 

 is made up chiefly of brownish-red grains presumably rutile, 

 clear grains supposed to be zircon and grains of epidote. A 

 portion of this heavy material was ground up in an agate 

 mortar and treated with KHS0 4 before the blowpipe. The 

 bead was dropped in hydrogen peroxide, giving the orange- 

 yellow color characteristic of titanium. The brownish-red grains 

 pretty certainly afforded the titanium, as epidote and zircon 

 were the only other minerals in the powder. Some of the grains 

 are striated. The brownish-red grains are therefore probably 

 rutile. A small quantity of this heavy powder was placed in 

 HF and H 2 S0 4 mixed in a platinum dish and digested in a 

 water-bath over night. All of the material was attacked by 



