File:Transactions of the Royal Society of New Zealand (1892) (14587682800).jpg

Identifier: transactionsofro92roya (find matches)
Title: Transactions of the Royal Society of New Zealand
Year: 1892 (1890s)
Authors: Royal Society of New Zealand
Subjects: Science
Publisher: Wellington, N.Z. : The Society
Contributing Library: Brigham Young University Hawaii, Joseph F. Smith Library
Digitizing Sponsor: Consortium of Church Libraries and Archives

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of felspar areporphyritically distributed. Some of these are over half aninch long, but as they crumble readily it is impossible to detachmore than mere fragments for examination. They show attimes a fine striation and glistening surfaces, but the cleavageis not well marked. The examination of the rock was conducted in twoways:— A. A chemical analysis of the rock as a whole, and of thefelspar separately. B. A microscopic examination by means of thin sections. A. Chemical Analysis.Portions of the rock were taken and ground up, so that aperfectly general sample might be obtained, and were analyseda number of times. Since the rock was roughly examinedfirst under the microscope a qualitative chemical analysis wasunnecessary, I show all the results obtained, with the excep-tion of those in No. III., as they were completely wrong, fromknown reasons. The last analysis is the most trustworthy,for reasons which I shall point out:— $nws*qthw* ^m gMmfo %nstiint$f Vol. xxv., pi,xlVi£. FifSl
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X40 Olivine> Andesite. Speight.—On an Occurrence of Olivine-andesite. 369 I. II. III. IV. Loss on ignition 2-97 3-16 3-13 3-13 Silica, Si02 ... 55-70 54-99 55-10 55-12 Alumina, A1203 21-10 20-96 20-41 Ferrous and ferric oxide 8-47 8-75 7-74 Lime, CaO 5-39 5-38 5-38 5-35 Magnesia, MgO 1-29 1-45 2-75 Soda, Na.,0 ... 3-72 3-94 4-03 3-80 Potash, K20 ... 2-66 2-66101-29 2-17 2-50 101-30 100-80 It will be noticed that the loss on ignition in No. I. is lessthan in the other cases. This was due to the fact that themineral was heated in an open crucible, and so the iron pre-sent in the ferrous state was oxidized to the ferric state; inthe succeeding analysis the powdered rock was heated in aclosed crucible, so that there might be no oxidization. Afterdetermination of the loss on ignition, the mineral was fusedwith fusion-mixture, and on extraction with HC1 the silica wasdetermined. The result obtained was high in the first case,owing to an error in weighing, care not being taken to pre-ve

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