£ 
42 The American Naturalist. [January,. 
and needles of the blue amphibole. In addition to these are tiny 
crystals of magnetite, sphene and zircon. In this matrix lie sheaves 
of the blue amphibole, which are formed of small needles or of large 
columnar crystals, sometimes measuring as much as 20 mm. in length. 
The crystals are well developed in the prismatic zone, where they ex- 
hibit clearly the cross section of amphibole. The plane of their opti- 
cal axes is the clinopinacoid. The extinction of the mineral is about 
13° to ¢, along the axis of greatest elasticity. The mineral must be 
closely related to riebeckite. A characteristic feature of the new am- 
phibole is its strong pleochoism, which is stronger even than that of 
glaucophane. =sky blue to dark blue; B= reddish to purplish- 
violet ; C= yellowish-brown to greenish-yellow. When broken, crys- 
tals of the blue amphibole are often healed with green actinolite, and 
often fibres of the latter mineral unite portions of blue crystals on. 
opposite sides of veins of albite cutting through the rock mass. An 
analysis of the blue mineral gave: 
SiO, Al,O, Fe,O, FeO. MnO MgO CaO Na,O K,O -H,O Total 
55.02 4.75 10.91 9.46 tr 9.30 2.38 7.62 .27 undet. = 99.70: 
This indicates a mixture of the three molecules Na, Al, Si,O,,, Na, 
Fe,” SO, and R”SiO, (where R is Mg: Ee:Ca=6: 2: iji in the pro- 
ene 1:2:9. The optical properties of the mineral are very simi- 
lar to those of the blue amphibole described by Cross.‘ Chemically, it 
lies between riebeckite and glaucophane. The author names it cross- 
ite. 
The Diorites, Gabbros and Amphibolites of Argentina.— 
The basic rocks from Argentine in the collection of Berlin University 
have been studied petrographically.by Romberg.’ They occur in the 
easternmost of the Cordilleran chains, associated with crystalline schists 
and eruptive rocks. The diorites and gabbros form stocks, and some- 
times sills and dykes, that are closely associated with gneiss and crys- 
talline limestones. The author divides the rocks studied into a num- 
ber of groups and sub-groups, recognizing as the two principal groups 
eruptive rocks, and those associated with the crystalline schists. Among 
the undoubled eruptives are gabbros and diorites, and of the latter 
class there are two varieties, the diorites proper and the quartz diorites~ 
Gabbro-diorites are also recognized among the specie: The gab- 
Of American Naturalist, 1890, P 1073. 
_ĉ Neues Jarb. f. Min. etc., B. B., ix, p. 293. 
