1894.] Mineralogy and Petrography. 59 
About 600 miles north of the Falkland Islands in the South Atlan- 
tic, a fall of volcanic dust occurred on May 26, 1892. Palache, who 
has examined some of the material, finds it to consist of fragments of 
glass and pieces and crystals of orthoclase, plagioclase, green hornblende 
and magnetite, with a very small quantity of what appears to be pyrox- 
ene. The character of the dust is thus andesitic. 
New Minerals..—Iddingsite has been known for some time as a 
` component of certain eruptive rocks from the far west, but not until 
Lawson’ discovered it in the carmeloite of California, had its character- 
istics been carefully enough investigated to warrant its receiving a 
name. As described by Lawson, iddingsite occurs as a pbenocryst with 
well-defined crystal outlines. It is of a bronzy color, has a very per- 
fect cleavage and a hardness of 2.5. Its cleavage lamellae are brittle. 
Before the blow-pipe+the mineral is infusible, though it loses water 
when heated. It is decomposed by acids after long treatment, but loses 
only its dark pigment, without alteration of its optical properties, when 
gently heated with hydrochloric acid. Maximum density = 2.839. 
Its crystals possess in thin section the habit of olivine. If the cleavage 
is regarded as pinacoidal, the other crystallographic faces are the prism, 
with a prismatic angle of about 80°, and another pinacoid, both of 
which are perpendicular to the cleavage. The elongation of the crys- 
tals is in the direction of the second pinacoid. If the cleavage is re- 
garded as parallel to the macropinacoid, 6 is in the cleavage plane, a 
is at right angles to it, and c is parallel to the elongation of the erys- 
tals. The plane of the optical axes is the brachypinacoid, and the min- 
eral is orthorhombic and negative; a = A, b6—Bande=C. In thin 
section the color varies between yellowish green and chestnut brown, 
and tbe absorption is strong parallel to e. The absorption formula is - 
C>B>A. The mean index of its fraction is low, and the double re- 
fraction strong. Qualitative tests showed the presence of silicon, iron, 
calcium, magnesium, sodium and water. In spite of the resemblance 
of its crystals to those of olivine, the author regards it as most probably 
an original separation from the magma that yielded the carmeloite. 
Mackintoshite is the name given by Hidden and Hillebrand’ to the 
original material from which the alteration product thorogummite’ is 
derived. Only a very small quantity was available forstudy. This is 
6 Amer. Geol., June, 1893, XT, p. 422. 
7 Bull. Dept. Geol. Univ. a. Nol L, P GE- 
8 Amer. Jour. Sci.. XLIV, 1890, p. 98. 
9 AMERICAN NATURALIST, Jan., 1893, p. 72. 
