REVIEWS. 
Economic Mrineranocy. By Tuomas Crook, A.R.CS., F.GS., 
M.I.M.M. pp. xi + 492, with 247 figures. London : Longmans, 
Green & Co., 1921. 25s. net. 
Ae the author states in the preface this volume is intended for those 
especially interested in the utilitarian side of mineralogy, he 
therefore contents himself with one chapter on crystal symmetry 
instead of the usual detailed account of all possible crystal 
forms given in textbooks of mineralogy. As the economic 
mineralogist seldom meets with well-crystallized minerals, the 
writer thinks this is a justifiable curtailment. 
The chapter on crystal optics is an unusually clear exposition of 
what is often a difficult subject to the student of mineralogy, and 
the same applies to the chapter on physical analysis, but the section 
dealing with flotation might have been improved if a simple 
apparatus for laboratory separation by flotation had, been described. 
Under the geology of mineral deposits the author gives a useful 
summary of the chief deposits of economic minerals arranged in order 
of age. 
The detailed description of the individual minerals is clear and 
complete, and the lists of the chief occurrences of the minerals 
of each metal are much more complete and detailed, than is usual. 
In the description of the use of the Westphal balance, no details 
are given of the use of the instrument for the determination of the 
specific gravity of a mineral fragment, nor is there any mention | 
of the use of the hydrometer for the determination of the density 
of a liquid which is certainly not often made use of in mineralogical 
work. 
At the end of the volume is a series of tables, the first of which 
gives the minerals in order of hardness with their chief physical and 
chemical properties, and with the refractive index and birefringence 
of the minerals with non-metallic lustre. It would have been useful 
to add these last details in the case of the minerals with metallic 
lustre which are transparent under the microscope. 
The last table gives the minerals grouped according to colour, 
but the fact of there being only six colour groups seriously affects 
its value as a help to determination. 
The illustrations are excellent, the photographs in most cases 
being taken from specimens in the Natural History Museum. 
EK. H. Davison. 
Curomium Orr. By W. G. Rumpotp. Imperial Institute Mono- 
graphs on Mineral Resources. 58 pp., with 2 diagrams and a 
map. London: John Murray, 1921. Price 3s. 6d. net. 
(VHE importance of chromium in the metallurgy of steel and the 
wide use of certain of its compounds in technology, have long been 
known, and the recent introduction of alloys of the stellite group 
