HANDBOOK OF THE METEORITE COLLECTIONS. 5 



2. Hexahedral irons: Homogeneous masses of nickel-iron with 

 evident cleavage parallel to the faces of a hexahedron and showing 

 lamellfB due to the twinning of a cube on an octahedral face. On 

 etching they show Neumann lines. These are divided into: (a) 

 hexahedral irons (H) ; (b) brecciated hexahedral irons (Hb) ; (c) 

 the Cape Iron group (Hca) ; (d) the Chester ville group (Hch). 



3. Massive irons: Amorphous irons showing neither Neumann nor 

 Widmanstatten lines or other structural features such as permit 

 satisfactory classification. Doctor Brezina has divided them into 

 five groups: (a) the Babb's Mill group (Db) ; (h) the Nedagolla 

 group (Dn) ; (<3)the Primitiva group (Dp) ; (d) the Senegal group 

 (Ds) ; (e) the Tucson group (Dt). 



MINERAL COMPOSITION. 



Though the elemental matter of meteorites may be the same as in 

 terrestrial rocks, the form of combination is at times radically differ- 

 ent and of a nature to indicate that they formed under conditions 

 quite unlike those existing on the earth to-day, and particularly so 

 with reference to the presence of free oxygen and moisture. 



The following list comprises meteoric minerals which are also con- 

 stituents of terrestrial rocks: Olivine, the orthorhombic pyroxene 

 enstatite (or hronsife), the monoclinic pyroxenes diopside and augite, 

 the plagioclase feldspars anorthite, labradorite, or oUgoclase, the 

 phosphate apatite, the oxides magnetite and chromite, the sulphides 

 pyrite and pyrrhotite, rarely the carbonate hreunnerite and various 

 forms of carbon including graphite and diamond. Those minerals 

 found rarely if ever in terrestrial rocks are the various alloys of 

 nickel and iron, to which the names kam.acite, taenite, and plessite 

 have been given, the nickel and iron phosphide schreiiersite, the iron 

 monosulphide troilite, the iron and chromium sulphide dauhreelite, 

 the iron protochloride lawrencite, the calcium and titanium (or zir- 

 conium) oxysulphide oshomite, the iron and nickel carbide cohenite, 

 the carbon silicide moissanite, an isotropic mineral believed to be a 

 re-fused plagioclase and called tnaskelynite, and asnnanite, a form of 

 silica. These are described in some detail, in alphabetical order, 

 below : 



Apatite. — The phosphoric acid reported in the numerous analyses 

 of meteoric stones has usually been considered a constituent of the 

 mineral apatite. As a matter of fact, crystals of this mineral in a 

 meteorite have been actually observed only by Berwerth, in the stony 

 portion of the Kodaikanal, India, siderolite. Recent investigations 

 have shown that the prevalent phosphatic mineral is not apatite, but a 

 mineral of nearly the same composition, differing in its crystallo- 

 graphic and optical properties, and perhaps identical with francolite. 

 Its exact nature remains yet to be ascertained. 



