Geology and Mineralogy. 251 



Si0 2 MnO CaO MgO A1 2 3 , Fe" 2 O a Alk. 



51-6 3-4 23-3 13"5 1'4 [6-8]=] 00. 



It seems to belong with the pyroxenes.— Jdhrb. Min., ii, 36, 1889. 



Pleonectite. A partially examined mineral from the Sjo 

 mines, Grythyttau parish, Sweden. It occurs in narrow veins 

 with arseniopleite ; color, grayish white; luster, greasy; hard- 

 ness, 4. Qualitative trials led to the conclusion that it was an 

 antimonio-arseniate of lead, carrying some chlorine. — Ibid., p. 40. 



5. Lehrbuch der Mineralogie von Dr. C. HrNTZE. Erstes 

 Lieferung, pp. 1-160, Leipzig, 1889 (Veit & Co.). — The publica- 

 tion of the first part of a new Descriptive Mineralogy which 

 promises to be, when completed, the most exhaustive work ever 

 written, is an event of no small importance to those interested in 

 this science. This great labor has been undertaken by Prof. 

 C. Hintze, of Breslau, and if the whole can be carried through 

 with the same care, accuracy and thoroughness exhibited upon 

 each page of this first part it will be a monumental work, reflect- 

 ing great credit upon its author and of great value to all workers 

 in mineralogy. The plan as announced contemplates the issue 

 of two or three parts yearly (at 5 marks each), the completion of 

 the whole in two volumes being accomplished in three or four 

 years. The present part forms the opening portion of the second 

 volume and is devoted to a part of the silicates, namely, those of 

 the olivine, willemite, eulytite, garnet, phacelite and topaz-anda- 

 lusite groups. Some idea of the fullness with which the species 

 are treated will be gathered from the fact that 13 pages are given 

 to olivine, 26 pages to topaz, etc. With topaz, for example, we 

 have first the crystallographic characters, the axial ratio, list of 

 forms, calculated angles, etc. ; then the physical characters and 

 optical constants very fully given with references to the original 

 papers ; then a review of the history of the species with respect 

 to its names, composition, etc. ; then follows a general statement 

 of method of occurrence, with a very minute description of all 

 the important localities, with an account of the crystals from each 

 and references to the authors who have treated of them. The fig- 

 ures of crystals are scattered through this part of the text as 

 referred to. An account of the artificial mineral and a list of anal- 

 yses, including also alteration products closes a most complete 

 and interesting chapter. Very little attempt is made at conden- 

 sation, and if this takes something from the compactness of the 

 whole it certainly adds to the clearness of presentation. 



The portion of the work at hand is too small to allow of a satis- 

 factory judgment in regard to the general classification to be 

 adopted, but it seems to follow the usually accepted methods. 

 Danburite is placed with topaz and andalusite, etc., though the 

 chemical composition does not show the same analogy that exists 

 in the form ; nephelite, however, is not included with the related 

 silicates KAlSiO,, LiAlSiO, NaAlSiO, since it deviates from the 



... 4 4 4 



unisilicate formula. We are surprised to find this last group 

 named after Scacchi's " phacelite," while the fact that Scacchi's 



