102 Pseudobrookite Crystals

The Geology and Petrography of Crater Lake National Park, 1902

 PART II.

BASALTS.

INTERSTITIAL BASALTS.

HYPERSTHENE, APATITE, AND PSEUDOBROOKITE CRYSTALS IN BASALT.

PSEUDOBROOKITE CRYSTALS.d

Accompanying the hypersthene in a single cavity were several slender, needle-like crystals, having a brilliant metallic luster. Their appearance and the association in which they occurred recalled the description of pseudobrookite as found in the hypersthene-andesite of Aranyer Berg, Hungary;e and, notwithstanding the minute size of the crystals, it was found possible to obtain approximate measurements from two of them, which seem to confirm this determination.

dThe description here given is the work of Dr. C. Palache.eAmong others, Traube, Zeit. für Kryst., Vol. XX, 1892, p. 327.

The forms found are shown in fig. K of Pl. XIV (p. 76) and in the following table, together with the measurements:

  Measured. Calculated. Number
of
readings
? p ? p
  o o o o  
a, 100 90 00 90 00 90 00 90 00 4
b, 010 00 00 90 00 00 00 90 00 4
m, 210 63 42 90 00 63 45 90 00 6
l, 110 46 00 90 00 45 23 90 00 3
e, 103 90 00 20 57 90 00 20 53 2

The faces of the pinacoids, a and b, were bright, but the prisms were deeply striated and gave very poor reflections.

The position here adopted is that originally proposed by Koch* and retained by Schmidt, Traube, and Groth. With Dana and Goldschmidt the axes b and c are interchanged. The former seems the more natural choice, in view of the pronounced prismatic habit of the crystals and since the chemical relations of pseudobrookite to brookite do not seem to bear out the apparent form relations between the two minerals which it was the purpose of the altered position to express.

*A. Koch, Min. Mitth., vol. I, 1878, pp. 77 and 344.
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