THE BOND SPRINGS STONY METEORITE 
53 
Three main types of chondrules are present : — 
(a) Monosomatic; composed of a single grain or crystal 
of enstatite or olivine. 
(b) Polysomatic ; consisting of several grains of one or 
more minerals segregated into conspicuous groups 
with glomero-porphyritic structure. 
(c) Cryptocrystalline ; with no determinable constituents 
or characteristic structures. 
Monosomatic chondrules are barred or laminated, parallel 
bars of enstatite (or olivine) in optical orientation alternating 
with laminae of gray, dusty material. The granular structure 
of other monosomatic chondrules is due to the gray, dusty 
material occurring as regularly arranged patches thi^ughout 
the single crystal composing the chondrule. These differences 
in appearance may depend on whether the chondrule has 
been sliced transverse or parallel to the laminae. 
Varieties of polysomatic chondrules are more numerous. 
Some enstatite chondrules or sectors of chondrules consist 
of fine fibres radiating from one or more points; others con- 
sist of larger sub-radiate crystals. Some porphyritic chon- 
drules are formed by several grains of olivine set in fine- 
grained indeterminate dusty material, or the dusty material 
may be absent and the grains of olivine crowded together, all 
extinguishing in different positions. Other chondrules 
consist of grains and fibres of enstatite in a fine-grained, 
base, or are made up of criss-cross fibres or fine-matted laths 
of enstatite in such a base. Composite chondrules contain 
both enstatite and olivine crystals in a microcrystalline to 
cryptocrystalline matrix; one consists of a core of fibrous 
enstatite surrounded by a ring of clear olivine grains, all 
components extinguishing in the same position. 
The cryptocrystalline chondrules, which often display 
undulose extinction, may consist of crystallites of enstatite : 
they are the least numerous type. 
Opaque Minerals. 
A polished section in reflected light reveals nickel-iron, 
abundant pyrrhotite, scattered ciystals of chromite, and 
occasional narrow veins of limonite. Intimately associated 
nickel-iron and pyrrhotite form irregular patches interstitial 
to the chondrules; they also occur as minute grains, 5 to 10 
microns across, sometimes in well defined rows, enclosed in 
the silicates. 
Before etching, the nickel-iron appears to be a uniform 
