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MINERALOGY: G. P. MERRILL 
ON THE MONTICELLITE-LIKE MINERAL IN METEORITES, AND 
ON OLDHAMITE AS A METEORIC CONSTITUENT* 
By George P. Merrill 
DEPARTMENT OF GEOLOGY. UNITED STATES NATIONAL MUSEUM. WASHINGTON 
Presented to the Academy. March 23. 1915 
It may be remembered that in 1883 Tschermak^ mentioned the oc- 
currence in many chondritic meteorites of an almost colorless constitu- 
ent occurring with very irregular outlines, in the groundmass, and exceed- 
ing in size the prevailing granules. These showed only traces of cleav- 
ages, were doubly refracting and optically biaxial though never showing 
good interference figures. The polarization colors were weak. It was 
found impossible to determine absolutely the mineral nature of the con- 
stituent, but it was suggested that it might be monticellite. Its pres- 
ence was noted in the Alfianello, Mocs, Knyahinya, and Mezo Madaras 
stones. The occurrence in the Knyahinya stone was later figured by 
him on plate 14, figure 3, of his Die Microskopische Beschaffenheit der 
Meteoriten. Since Tschermak's writing the mineral has been noted by 
various authors. Lacroix^ describes in some detail what is unquestion- 
ably the same mineral in the stone of St. Christophe la Chartreuse. He 
finds it possessing two easy but interrupted cleavages, cutting at an 
angle of about 60°, with a birefringence less than 0.003, which he notes 
is less than that of olivine and superior to that of feldspar, with which 
it is often found in contact. He also was unable to determine its exact 
nature optically, or to separate it by means of heavy solution, but noted 
that it could not be monticellite on account of its low birefringence. 
He further noted its occurrence in the meteorites of Chantonnay, d'Au- 
male, de Barbotan, de Salles, de Berlanguillas, and Lancon. The 
present writer recognized the same mineral in sections of the meteorites 
from Rich Mountain, N. C.,^ and Felix, Alabama,^ and though recog- 
nizing its biaxial nature and weak birefringence was likewise unable 
to identify it absolutely. Still later, Borgstrom recognized it in the 
meteorite of St. Michel,^ and was able to determine the positive char- 
acter of the acute bisectrix. 
In connection with his work on the minor constituents of meteorites, 
the present writer had opportunity for examining numerous occurrences 
of the mineral, and it was decided if possible to determine its nature or 
at least to carry a knowledge of its properties one step farther. Unable 
by the means at his command to fully satisfy himself regarding all its 
* Published with the permission of the Secretary of the Smithsonian Institution. 
