178 
MINERALOGY: G. P. MERRILL 
often with mental reservations, maskelynite. The material first described 
under this name, it will be remembered, was found as a prominent con- 
stituent of the meteorite of Shergotty, and was sufficiently abundant to allow 
a satisfactory determination of all of its properties, including chemical com- 
position. All occurrences since noted are of microscopic dimensions — mere 
interstitial areas of rarely more than two or three millimeters in diameter, 
and determinable properties so nearly negative that the referring of the min- 
eral to maskelynite has been more in the nature of an acknowledgment to the 
quality of Tschermak's work than to actual determinations on the part of those 
describing it. This certainly was true in my own case, 4 and it was not until 
I was studying the stone of Holbrook, Arizona (1912), that I separated par- 
ticles and by the recently introduced immersion method determined the 
index of refraction to be 1.51, which, according to Larsen's tables, is that 
of an oligoclase glass. Since that writing I have followed up the matter as 
systematically and thoroughly as time and opportunity will permit, and 
have reached the conclusion, pronounced without hesitation, that the min- 
eral is in all cases feldspathic, ranging in composition from oligoclase to an- 
orthite, and owes its condition to a fusion since the original crystallization of 
the stone, followed by a cooling too rapid to allow it to regain its normal 
properties. 
These conclusions are based upon examinations of a large number of sec- 
tions in which I have found the mineral in all stages from a glass essentially 
isotropic with the low index (1.51) mentioned above to one plainly biaxial 
but without crystal outlines, cleavage, or other recognizable properties, with 
indices of 1.543 and 1.545, and in one case (Ness Co.) 1.56. Also, in forms 
where the mineral is largely isotropic but still retains, in places, traces of 
plagioclase twinning. It is this last feature, it should be stated, that causes 
me to consider it a re-fused feldspar, rather than a residual and original 
feldspathic glass. 
These observations, it will be observed, are supplemental and corroborative 
of those of Tschermak. 5 The subject seems worthy of this extended notice, 
not merely on account of the new observations, but since Farrington in his 
recent Meteorites remarks concerning the mineral that "Its exact nature is 
yet to be determined." 
Attention should be called, in this connection, that an elevation of tem- 
perature sufficient to fuse a feldspar without at least partial destruction of the 
olivine would be impossible but in an atmosphere completely devoid of all 
oxidizing gases. (See further under Effects of Heating, below.) 
4. Effects of Heating Meteoric Stones at Various Temperatures. — The fact 
that Meunier had transformed meteoric stones of his aumalite group into 
tadjerites, by heating to redness, suggested the availing myself of oppor- 
tunities offered by the Pennsylvania Zinc Company at their works at Palmers- 
ton, Pennsylvania. A series of prepared specimens, including two cubes, 
one each of the Estacado and Homestead meteorites, some 10 mm. in di- 
