220 J. S. Diller — Mineralogical Notes. 



basalt from Hochbohl by Owen, it is frequently grouped with 

 the magnetite. In the Kentucky rock, however, the perofskite 

 is so intermingled with dolomite and other secondary products 

 as to suggest that it belongs in the same category. It is not 

 found included in the central portions of ilmenite grains nor 

 in fact in any of the primary minerals as if present at the time 

 of their crystallization, but occurs only under such circum- 

 stances as to lead to the conjecture that it may have originated 

 subsequently from the alteration of the ilmenite. 



This opinion is rendered less probable when we remember 

 the pyrogenous methods employed in the artificial production 

 of perofskite, and recall the fact of the chemical stability of the 

 ilmenite which occurs abundantly with pyrope in the sand re- 

 sulting from the disintegration of the peridotitic rock. 



In the same sand with the pyrope and ilmenite a lameller 

 monoclinic pyroxene is sparingly found. The crystals are not 

 simple as those of enstatite previously noted, but made up of a 

 multitude of twinning lamellse lying parallel to the orthopina- 

 coid along which it may be readily split. Some of these pyrox- 

 enes are dull but others are clear greenish yellow like olivine. 



A part of this olivine rock is holocrystalline granular like 

 the dunites, but a much larger portion than was at first sup- 

 posed is decidedly porphyrinic. Numerous crystals of olivine, 

 many of them idiomorphic, are embraced in a ground mass 

 which has been greatly altered since its consolidation. This 

 rock plainly belongs to the type which the late Prof. H. Car- 

 vill Lewis (Eept. of British Assoc, for Adv. of Sci., 1887, p. 

 721) designated kimberlite, and which Prof. Rosenbusch classes 

 among the Pikrite-Porphyrites (Der Massigen Gesteine, 2 Ed., 

 1887, vol. ii, p. 519). 



3. Gehlenite in a Furnace Slag. 



Numerous square prisms of gehlenite occur in furnace slag 

 found near McYille, Armstrong, Penn. ; accordingly in the 

 thin section it appears square or oblong rectangular. The iso- 

 tropic square sections are readily found to be uniaxial and neg- 

 ative. Spherical liquid and rod-like inclusions are numerous. 

 Cleavage lines are not conspicuous. The easy gelatinization of 

 the mineral in hydrochloric acid and its difficult fusibility be- 

 fore the blowpipe readily distinguish it from similar miner- 

 als. Although not previously reported as occurring in this 

 country, gehlenite is probably one of the most easily obtained 

 specimens to illustrate the optical properties of quadratic min- 

 erals in thin sections and on this account alone is worthy of 

 notice. 



