Febbuaet 21, 1908] 



SCIENCE 



313 



Blasdale's determination is a very acid titano- 

 silicate of barium possessing the following 

 properties: It varies in color from dark blue 

 through light blue to colorless, this property 

 having led to the original belief that the gem 

 was sapphire. The pleochroism is very 

 marked, the ordinary ray being colorless, while 

 the extraordinary is blue, with a violet tint 

 when intense. The absorption is e > 0. The 

 refractive indices are high, = 1.7Y, e = 1.80, 

 in sodium light. The double refraction is 

 therefore very strong and the mineral optically 

 positive. Benitoite crystallizes in the hexag- 

 onal system, trigonal division, the most com- 

 mon habit being pyramidal. The individual 

 crystals are usually less than a centimeter in 

 maximum diameter, although they occasion- 

 ally attain a size of 2.5 centimeters (one inch). 

 The hardness is 6 J to 6 J, or below quartz; the 

 density is 3.64 to 3.65. The mineral fuses at 

 about 3, is almost insoluble in hydrochloric 

 acid, quite easily attacked by hydrofluoric 

 acid, and dissolves readily in fused sodium 

 carbonate. Associated with the benitoite is a 

 black or brownish-black prismatic mineral 

 which Dr. Louderback believes to be new, and 

 to which he has given the name carlosite.' 



Benitoite and carlosite occur as individual 

 crystals associated with veins or geodes of, a 

 white zeolite (which Mr. W. T. Schaller has 

 identified as natrolite), in a great schist lens, 

 enclosed by one of the largest areas of serpen- 

 tine found in the Coast Range of California. 

 This serpentine mass occupies five or six miles 

 of the crest of the ridge north of White Creek 

 in the western part of Fresno County, twenty- 

 five miles northwest of Coalinga, and extends 

 northwestward at least four or five miles into 

 San Benito County. Many irregular lenses 

 and masses of schist and several kinds of more 

 or less basic igneous rocks are associated with 

 the serpentine. The particular schist lens 

 containing the gem mineral cuts through a 

 low hill of serpentine at the bend in one of 

 the headwaters of the San Benito Eiver. The 

 lens is about 150 feet wide at its widest 

 part, at least 1,200 feet long, strikes about 

 N. Y0° W. and appears to dip N. 20° E. at 



'Op. cit., p. 153. 



angles varying from 70° to 80°. The rela- 

 tions are best studied in the shallow cuts, 

 which comprise the present development works, 

 and which are confined largely to the middle 

 of the southeastern portion of the lens. 



The country rock of the gem-bearing natro- 

 lite veins is a schist containing glaucophane, 

 and varying in color from dark greenish gray 

 to a rather light blue. Near the lower or 

 southwestern contact with the serpentine (the 

 latter being soft, light-colored and containing 

 numerous thin, flaky asbestos veins) the schist 

 is dark greenish, fine-grained, and breaks with 

 a sharp-edged angular fracture. It contains 

 veins up to three eighths of an inch in thick- 

 ness, of a light greenish mineral, resembling 

 chlorite, which can be scratched with a knife. 

 The joint faces are coated with thin films 

 having the characteristics of manganese oxide. 

 A peculiar-looking mineral, somewhat resem- 

 bling iron pyrites in appearance, but quite soft, 

 occurs sparingly in thin veins throughout this 

 part of the lens. Some faint copper stains 

 were also noted at one place. In the imme- 

 diate vicinity of the gem-bearing veins toward 

 the middle of the schist area the rock is blue, 

 h^s been considerably altered, probably by the 

 waters carrying the vein and gem-forming 

 materials, and breaks with a fine, granular 

 fracture exposing component crystals discern- 

 ible with the unaided eye. The schist adja- 

 cent to the veins is often largely replaced by 

 natrolite. The planes of schistosity are more 

 plainly visible in the bluer variety, which is 

 apparently the richer in glaucophane. Where 

 extremely weathered and wet the altered schist 

 has the appearance and feel of a tough blue 

 clay. Weathered surfaces of the schist are 

 rough, sometimes being covered by mammilli- 

 form nodes. This nodular occurrence is also 

 encountered below the surface in the more 

 weathered and porous portions of the rock. 

 The color of the weathered surfaces is bluish 

 gray to reddish brown, the latter due to iron 

 oxide. The schist usually weathers faster 

 than the natrolite or benitoite and seems to 

 have been protected over those areas which 

 once formed the wall or is at present covered 

 with the remains of a natrolite vein. On one 



