
Petrological Description of the Mokoia Aerolite.
Mr. R. Speight, M.A., B.Sc., Lecturer in Geology, Canterbury College, forwarded me the following report: “Macroscopically the stone is of a black-grey colour, with small rounded chondri of whitish appearance

plainly visible. The determination of the specific gravity of a fragment gave a result 3.41, which is somewhat low; but this meteorite is remarkably vesicular, which makes is appear lighter than it really is. However, the graphite constituent points to the former existence of a hydrocarbon, and meteorites with hydrocarbons appear to be noted for their low specific gravity. Under the microscope it shows the following characters: It consists largely of a groundmass of dark unindividualised matter, which contains numerous irregular crystal fragments of small size, consisting chiefly of olivine, and occasional patches of brownish glass full of bubbles and black dust. In this base are numerous chondri up to 1.5 mm. in diameter, usually rounded and distinct from the groundmass, but at times ill-defined and grading into it. Some of the patches are cloudy and indefinite in character, but obviously of crystal particles. Many of the chondri show a nucleus of coarser grain, with a halo of smaller grains between it and the surrounding base. When enstatite is present they usually exhibit a fibrous structure. They are composed chiefly of olivine fragments, which are brecciated and irregular in shape, much fissured by cracks, clear as a rule, and containing rounded black grains and bubbles, apparently of gas. The size of the fragments is tolerably uniform in each chondrus, with the exception of those showing the halo, and they grade downward from 1 mm. in length to those which can only be separated by higher powers of the microscope. Augite and also enstatite are present, some of the chondri being composed exclusively of the latter mineral arranged in sheaf-like aggregates, but it occurs frequently associated with olivine in the same chondrus. Small fragments of feldspars are occasionally seen with fine twinning of the albite type. The only means of determination that could be employed was Michel-Levy's method, and from the small number and size of the fragments even this was not altogether satisfactory. There were several small extinction-angles, but they ranged as high as 27o, corresponding to an acid labradorite. Anorthite appears to be the common feldspar of meteorites, though others have been observed occasionally. The chemical analysis shows that the rock contains no potash, but 2.86 per cent. of soda, and this may have come from soda-bearing feldspar, as none of the other minerals present are usually alkaline. Some of the chondri contain a small quantity of glass, occasionally as a kind of nucleus, and in one case it has apparently corroded the olivine crystal where it has been in contact with it. This is the only evidence which I have been able to find which points to a high temperature preceding the final consolidation of the meteorite. The phenomenon is an isolated one, and the brecciated structure of the chondri with their interior of larger fragments surrounded by a row of smaller ones, as well as absence of melting on the edge of the fragments, distinctly suggests that this has not been the case, or, if it has been, the rock has cooled very quickly. I was unable to detect with certainly in the specimen at my disposal any of the sulphides or native elements usually occurring in meteorites, and no doubt it belongs to that class usually designated as 'stony.’”
Dr. P. Marshall, Professor of Geology, Otago University, Dunedin, to whom I gave a fragment of the stone, sent me the following remarks: “As you anticipated, it proved a very difficult matter to make a section of the piece of the meteorite that you gave me. However, I send you the result. The clear crystals are olivine, and the spherules are, I fancy, formed of radiating crystals of the same mineral. There is a very little native iron. By far the greater portion appears to be magnetite. The magnet will lift

quite large pieces of the meteorite, and the mineral is perfectly opaque, so I have little doubt as to its nature.”
In conclusion, I should like to express my indebtedness to all those who have so willingly assisted me, especially Mr. C. Hawken, Mokoia; Mr. J. L. Fletcher, British Museum, London; Mr. A. Hamilton, Wellington; Mr. J. T. Ward, Wanganui; Mr. R. Speight, M.A. Christchurch; Dr. P. Marshall, Dunedin; Mr. B. C. Aston, Wellington; and Mr. W. Syme, Wanganui.
