[2(j NEPHRITE AND JADEITE. 



Traces of manganese were found in both samples. 



01 these jades, the first was line in color, texture, and translucency ; 

 the second was coarse, mottled, and opaque. The one approximates in 

 composition to normal jadeite, the other varies from it both in compo- 

 sition and density. 



Under the microscope the Sardinal specimen appears as a finely 

 granular aggregate of colorless crystals, none of which possess perfect 

 crystalline outlines, because of mutual interference. The texture is 

 verv uneven, scattering and clustered forms, from 0.1 to 0.5 mm in diam- 

 eter, being distributed irregularly through a ground-mass composed of 

 minute granules and scales which between crossed nicols blend into 

 each other without distinct lines of separation. The mineral is almost 

 perfectly colorless in the thin section or with a very faint greenish tinge 

 and non-pleochroic, but polarizes in brilliant red, yellow, and purple 

 colors. It is rendered slightly impure through inclosures of innumer- 

 able minute black and brownish dust-like particles the nature of which 

 a power of seven hundred and fifty diameters fails satisfactorily to 

 determine. 



The larger forms show two well-developed cleavages which in basal 

 sections cut each other at approximately right angles. An optic axis 

 lying in the plane of symmetry appears in both basal and orthopina- 

 coidal sections. The angle of extinction for section parallel to ooP 

 oc=0° ; and for those parallel to ooPx varies from 35° 40°. These 

 are properties common to the mouocliuic pyroxenes, and would not in 

 themselves alone indicate decisively any one particular variety. 



Krenner,* who has studied jadeites of similar composition and struct- 

 ure from Burmah, claims as a result of his examinations and the anal- 

 yses of Damour, that the mineral is a soda-spodnmene. 



The Oulebra jadeite, 28992, differs structurally from the last (59927) 

 in that it is made up largely of an aggregate of elongated and irregular 

 scales and fibers compactly matted together, in which the individual 

 scales blend into one another as the stage is revolved. It seems to cor- 

 respond to the " StengelfaserUf aggr-egate of the Germans. Through- 

 out this scaly fibrous ground-mass are scattered occasionally larger and 

 very irregular forms wholly without crystal outlines and rarely showing- 

 cleavage lines. All are colorless and non-pleochroic, and both large 

 and small give extinction angles varying from 29° to 40°. 



The descriptions given above agree closely with those of other observ- 

 ers. M. Cohent describes a jadeite from Thibet as a granular aggregate 

 of crystalsof a mineral belonging to the pyroxene group and of omphacite- 

 like habitus. The crystals show a nearly rectangular cleavage, give 

 extinction angles of 41°, and show an optic axis in both orthodiagonal 

 and basal sections. Fluidal inclusions were observed and occasional 



' Vims Jahrb., etc., 1883,11, 1st H., p. 173. 

 t N. Jabr. f. Mia., etc., 1884, 1 B.,1 Heft., p. 71. 



