1092 The American Naturalist. [December, 
found in America. They are transparent, yellowish, and in size the 
largest measure 3 x 2.5x2 em. Their habit is prismatic parallel to a, 
and each individual is bounded by many faces. 
In and upon calcite crystals lining some of the geodes of Keokuk, 
Iowa, Keyes" announces the discovery of very handsome tufts and 
radiating masses of millerite. 
Beds of specular hematite, intermixed with martite, are reported by 
Hill* as abundant at the junction of diorite and limestone in many 
localities within the State of Coahuila, Mexico. 
Physical Properties of Minerals.—A series of new determina- 
tions of the specific heat of boracite at different temperatures is reported 
by Kroeker.? The materials experimented upon were four transpar- 
ent crystals from Linneberg, one piece being from a large crystal with 
a cubical habit, and the others fragments of dodecahedral crystals. In 
all cases it was found that the specific heat of the mineral varies with 
the temperature, and that the increment of variation increases rapidly 
between 250°-270°. Below 270° the cubic and the dodecahedral 
crystal gave similar results, above this temperature the results are dif- 
ferent. For details of the experiments the reader must be referred to 
the author’s paper. 
Two articles of interest to mathematically inclined physical miner- 
alogists are the one by Pockels” on the changes effected in the optical 
characterists of alum and beryl by pressure acting in a single direction, 
and the other, by the same author,” on the elastic deformation of piezo- 
electrical crystals in the electrical field. 
Traube" finds that the following compounds, all of which form 
dextro-rotatory solutions, are hemi-morphie, viz.: Sr (SbO),(C,H,0,), - 
Pb(SbO),(C,H,O,), and Ba(SbO),(C,H,O,),+H,O. All are also tetar- 
San ee strontium me legal ‘compounds being the first examples 
of h erystallizing in the hexagonal 
system, and the barium salt the first instance among tetragonal bodies. 
" Amer. Geologist, XI, p. 126. 
** Amer. Jour. Sci. XLV, p. 111. 
? Neues Jahrb. f. Min., etc., 1892, p. 125. 
? Neues Jahrb. f. Min., etc., B. B. VIII, p. 217. 
?. Ib. B. B., VIII, p. 407. 
? Tb. B. B., VIII, p. 269. 
