576 The American Naturalist. [June, 
vertical axis, and are flattened in the direction of the macropinacoid. 
Like wohlerite, nearly all hiortdahlite crystals are twinned. In 
the latter case the twinning plane is at right angles to the vertical axis, 
and the combination face is the macropinacoid. ‘The axial angle 
is large. The optically positive first bisectrix is EL inclined to 
the vertical axes. The extinction on the œ Pæ is 25° and on œ P% 
is about 15314°. No well marked cleavages are observed in any sec- 
tions. The specific gravity is 3.235—3.267, and the composition : 
SiO, TiO, ZrO ZrF,O Fe,O, FeO MnO CaO MgO Na,O H,O 
$3.60 3:50 9.65 22,00 34 94 90 32.53 .¥O 6.53. .5§8 
Cappelinite, the discovery of which was announced some years ago 
by Brogger, occurs in hexagonal prisms with œ% P, 4 P and P. a:c: 
==1. : 1.2903. Their double refraction is negative and their composi- 
tion is as follows: 
SO BLO, Y,O, LaO, CeO, Tho, BaO CaO Na,O K,O Loss 
44,660 36:98 52.62'°2:97 -1.20 8 8.29 67 -.53...::22 «Gly 
corresponding to the molecular combination of R,I¥Y(SiO,), and 
R1!Y(BO,),. The hardness of the mineral is 6, and its specific gravity 
is 4.407. It is regarded as a member of the melanocerite group, to 
which also the following named mineral is supposed to belong. This 
mineral, aryocerite, is likewise hexagonal. Its axial ratio is r : 
1.1845, and its specific gravity 4.295. It differs from melanocerite in 
containing much more cerium and thorium (CeO, and ThO,). It 
occurs in nut-brown tables with a rhombohedral habit. Wetbyeite 
occurs in small crystals with a tetragonal habit. In form they 
resemble zircon, but are really orthorhombic, as their optical 
investigation oe with the vertical axis that of least elasticity. æ- 
: ¢=.9999 : 1: .64. It was impossible to separate the mineral from 
the pairsite doita with it, but an analysis of the mixture leads to 
the view that weibyeite corresponds in composition to the formula 
[(Ce,La,Di)F],(CO,),.——Barkevikite, although long known as a 
_ variety of hornblende, has received but little attention in recent years. 
A new analysis shows it to have the following composition : 



TiSiO, Al,O, FeO, FeO MnO CaO MgO NaO K,O 
42.46 11.45 6.18 19.93 .75 10.24 1.11 6,08 1.44 
Although chemically not very different from arfvedsonite, its physi- 
cal properties readily distinguish it from this species. The extinc- 
tion is 1234 in the acute £, while in arfvedsonite it is in obtuse £. 
