161 



METEORITES, t 



The Earth, in its orbit crosses the paths of swarms of stones 

 that are also revolving round the Sun. When a portion of such, 

 a swarm comes within the sphere of the Earth's attraction, some 

 of the stones are drawn out of their course, fall to the surface 

 under the influence of gravitation, and are known as Meteorites. 

 By friction with the earth's atmosphere such stones become 

 incandescent, and are hence known as " shooting stars." No 

 element has as yet been found in meteorites not already known 

 as existing in the Earth's Crust. The most noteworthy point in 

 their composition is the frequent presence of metallic iron 

 alloyed with nickel. There is a complete gradation from 

 meteorites composed almost entirely of metallic iron, and having 

 a specific gravity of over 7, to stony varieties containiDg little or 

 no iron, and consisting of such well-known minerals as olivine, 

 enstatite, &c. These stony meteorites closely resemble some of 

 the "ultra-basic" igneous rocks. Metallic iron has also been 

 found in basalt. Meteorites are classified according to the 

 relative proportions of the metallic and stony constituents. 



The collection of meteorites will be found in a special case 

 immediately opposite the entrance ; while the Mungindi iron 

 stands in a small case by itself in the central passage. 



The series of specimens and polished slices of foreign meteor- 

 ites is arranged after the classification of Dr. Brezina, and will 

 be found on the upper shelves. This classification depends 

 upon the character of the figures ( Widmanstdtten) which are 

 produced when a polished surface of an iron meteorite is etched 

 with acid.* A special slice, coloured to explain the terms used 

 in describing these figures, will be found on the top shelf. 



The New^ South Wales meteorites represented here are the 

 Cowra, Bingera, Temora, Moonbi, and Mungindi, They are all 

 iron varieties, and, with the exception of Bingera, belong to the 

 octahedral division. 



* The explanation of the production of these regular figures is that the meteoric irons 

 «ontain different alloys of iron and nickel, which are arranged crystallographically and are 

 attacked by acids with unequal intensity. 



t The objects known as obsidian buttons are now regarded as of cosmic origin, and will in 

 future be exhibited with the meteorites (.see page 172). 



