264 
than the stony varieties. An iron me- 
teorite is readily attracted to a magnet, 
but of course so is ordinary cast iron, 
as well as some varieties of iron ore. 
If the specimen has the characteristic 
external features of a meteorite referred 
to above, it should be investigated. 
Hit the sample with a hammer to 
see if small pieces can be broken off. 
If the fragments removed have a 
brownish or black color, test it further 
by pounding it upon a rock or anvil. 
Iron ores are brittle, and hence easily 
reduced to a powder, which may be 
brown, red, or black depending upon 
which of the iron minerals has been 
found. Both meteoric iron and manu- 
factured iron are very tough, and 
pounding with a hammer does not 
affect them much. Samples not af- 
fected by pounding should be tested 
with a file or whetstone, either of 
which will develop a silvery-colored 
spot if the sample is a metal. 
The finding of any metallic object 
suspected of being a meteorite should 
be checked by someone familiar with 
the identification of meteorites. Cut 
a small protruding portion from the 
mass with a hacksaw and send it to 
some institution engaged in the study 
of meteorites, together with informa- 
tion concerning the locality where the 
specimen was found. 
If the person finding the iron is 
experienced and equipped to make 
certain specific tests, the metal can be 
ground down until a polished surface 
is obtained and this etched with dilute 
nitric acid. Repeated etchings are 
made until the structural pattern is 
developed on the polished surface. 
If the specimen being tested is a 
meteorite, it will probably have struc- 
tures similar to those shown in the 
illustrations in this paper (pls. 3, 4, 5). 
Another chemical test which it is 
worth while to make is that for nickel, 
as all metallic meteorites contain 
nickel. Persons making the etch test 
should have their results checked, as 
the etch structures of meteorites are 
variable, and some of the rarer types 
of meteoritic irons could easily be 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
overlooked if only etch tests are made. 
There are several kinds of iron 
meteorites, the various types being 
identified by the different etch pat- 
terns displayed. The simplest type is 
the hexahedrite, which consists of only 
one phase of iron and nickel and is 
usually characterized by a well-devel- 
oped series of Neumann lines (pl. 3, 
b). This group contains about 5.5 
percent nickel, and when the percent- 
age of nickel is no greater, the iron is 
capable of retaining the nickel in 
solution; hence, hexahedrites consist 
of a single alloy of iron and nickel. 
Meteorites with higher percentages 
of nickel have two alloys present, one 
of which has the same composition as 
the hexahedrite and is called kamacite, 
and the second, richer in nickel, is 
known as taenite. These alloys sepa- 
rate out into platy structures resem- 
bling the habit shown in plate 4. This 
structure is known as a Widmanstat- 
ten pattern, and a meteorite with this 
habit is classified as an octahedrite 
(pl. 4). Meteorites having higher per- 
centages of nickel usually have nar- 
rower bands of kamacite; hence octa- 
hedrites may be subdivided into 
coarse, medium, and fine, depending 
upon the width of the kamacite bands. 
Some metallic meteorites, when 
etched, lack a well-developed struc- 
ture; these are called ataxites (pl. 5, 
a). They have an etch pattern which 
those inexperienced in meteorites 
might fail to recognize. 
There are meteorites which contain 
almost equal quantities of stony and 
metallic constituents. One such ex- 
ample is a pallasite (pl. 5, b) consisting 
of a silicate mineral, olivine, which is 
enclosed in a network of metal. 
Stony meteorites are heavy because 
the principal component minerals, 
pyroxene and olivine, have specific 
gravities slightly over 3, and also 
because most of them contain an ap- 
preciable percentage of metallic in- 
clusions. Beneath the outer crust of 
a stony meteorite is usually founda 
fine-grained aggregate of minerals. 
These may or may not be firmly bound 
