1890.] Mineralogy and Petrography. 573 
Single crystals are described, and twins following four twinning ` 
laws are well illustrated in the plates. The optical properties of the 
mineral are briefly sketched. Several varieties of garnef are mentioned, 
two analyses of which are worth recording. The black-green garnet of 
Stok6 and the yttrium garnet of the same localiy contain resectively : 
SiO, TiO, Al,O, FeO, Mn,O, Y,O, MnO MgO CaO -Na O HO 
34.90 8.97 20.43 DAO Ge Ae ae 1.27 
34.52 2.98 eOr 26.68. 2.15.35 38 e -79 -43 
Nordenskjéldite, with an axial ratio of a: 21, has a com- 
position corresponding to Ca (BO), SnQ,, or aia as the result 
of new measurements, is concluded to be orthorhombic with a: ġ : c= 
1.0098: 1: 4.7556. Its fracture figure (on the perfect cleavage par- 
allel to œ% Pos) consists of two lines crossing each other at angles of 
about 81° and 98°, the smaller of which is bisected by the vertical axis. 
The gliding planes correspond very nearly to those of the dome } P- 
The axial plane is the base, with 4 the positive acute bisectrix. Anew 
analysis of carefully purified material shows slight differences from the 
previously published analyses, and corresponds closely to the formula 
R,” RJ Ti (SiO), Zeucophane crystals to the number of twenty gave 
good enough reflections to enable Brégger to determine without diffi- 
culty their orthorhombic symmetry, @ : 6 : c=.9939 : I : .6722. 
The axial plane is the macropinacoid and ¢ is the negative acute bisec- 
trix. 2Ena==74° 15’. MMelinophane crystalizes in the tetartohedral 
division of the tetragonal system, Optically it is uniaxial. Chemi- 
cally it differs from leucophane [Na, (F Be), Ca, (SiO,),] in containing 
more beryllium [i. e. it is Na,(FBe), (Ca,O), Be, (SiO,),]. A thor- 
ough discussion of the characteristics of acmite and egerine leads to 
the view that they are well marked varieties of the same pyroxene, 
closely related to diopside. Acmite is nearly always twinned, while 
ægerine is usually in simple crystals. Lévenite according to the most 
recent measurements has æ : 6: c—=1.0963: 1: .7151 and S=69° 4214’. 
Wöhierite usually occurs in twins, whose twinning plane is the ortho- 
pinacoid. When placed in the conventional position for pyroxene its 
axial ratio becomes æ : } : c==.9966: 1 : .3547 with S==89° 18’ 50.” 
Its absorption is C > B=A, and pleochroism varies between yellow 
and colorless shades. Lavenite and Wohderite are regarded as zircon- 
ium pyroxenes, closely related to the corresponding triclinic pyroxene 
hiortdahlite. Polymignite crystals are orthorhombic, as is well known, 
with the axial ratio .7121 : 1: .5121. Their hardness is 6-6.5, and 
density 4.77-4.85. Chemically and morphologically the mineral is 
