1890.] Mineralogy and Petrography. 575 
27”. It occurs in tabular crystals, with a perfect cleavage parallel to 
the base ; a hardness of 6 and a specific gravity of 2.553. The extine- 
tion in co P% is inclined 581° to c and 27° 45’ to the clearage paral- 
lel to oP. 2V, —29° 55’ for sodium light. Very exact measurements 
of a large number of natrolite crystals from Little—ar § indicate that 
the mineral is monoclinic with æ : 4 - ¢=1.0165 : I : 1.3599, and p= 
89° 54’ 52”, and not orthorhombic as is usually assumed. The ortho- 
rhombic symmetry, which is ordinarily observed, is due to twinning par- 
allel to the orthopinacoid. These monoclinic natrolites differ from 
the ordinary orthorhombic form in containing a small quantity of 
potassium. ‘The extinction angle increases with the potassium con- 
tent. Bergmannite and brevicite are shown by the author to be either 
natrolite, or mixtures of this mineral with several other substances, 
New Minerals.—Hambergite. A single specimen of this mineral 
is of grayish white color, and is orthorhombic with oo P, œ Pa, œ P% 
and oP. a: 6: c=.7988 1: .7267, and hardness=7.5. Se. Graz 
2.347. Plane of the optical axes is œ P, & and ¢ is the acute 
bisectrix. 2Vna— 87°7 (observed) or 87° 40’ (calc.). Analyses 
yielded : BeO=53.25% ; H,O=10.03 ; B,O,=36.72 ;==(HO) Be,BO,. 
_Johnstrupite was originally confused by Brogger with mosandrite, 
which it resembles in many respects. Careful observation shows its 
axial ratio to be a: 5: c—=1.6229: 1: 1.3594- 8=86° 5534’, and 
the plane of its optical axis the clinopinacoid, with the positive acute 
bisectrix inclined 234° to ¢, in which it closely resembles mosandrite. 
The latter mineral however is reddish brown when fresh, while john- 
strupite is brownish green. That they are two distinct minerals is 
shown by their composition, which corresponds respectively with the 
formulas (OH),F,H,,R,Na,CayCe,(SiO,)r» for mosandrite, and F,H,R, 
Na,Ca,,Ce,MgAl(SiO,),, for johnstrupite. The similarity in composi- 
tion and morphological properties between these two minerals and epi- 
dote leads the author to regard them as members of same group. 
Calciothorite is a deep reddish brown amorphous substance, with a hard- 
ness of 4.5 and a sp. gr. of 4.114. Its composition is : 
SiO, ThO, C&O, Y,O, AlO, Mn,O, CaO MgO Na,O H,O 
Wate cosh. an, see tee ea 698 94, a BSD 
corresponding to 5ThSiO, 2[Ca,SiO,]+ca. 10H,O. Hiort- 
dahlite is a triclinic pyroxene occurring in small, thin, tabular crys- 
tals of a yellowish or yellowish brown color Its crystallographic 
constants are a : 4: c—=.9981 : I: -3537 a—89° 30' 57”, B=90° 29’ 
6, y=90° 6 10”. The crystals are elongated in the direction of the 




