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Synopsis It is well known that due to the rapid advances made in the understanding of the materials behaviour, metals and alloys, inorganic and organic materials and pharmaceuticals (to cite a few) can be bought by giving detailed specifications. The suppliers, in turn, produce test certificates to describe their materials with adequate precision. The situation is not quite the same when one wants to buy a gemstone! To quote from the book 'A green garnet or diopside could visually appear like an emerald. There is, however, a vast difference in the price of the two. Similarly, the difference in the value of natural and synthetic stone which look alike . . . could be in the ratio of 1 : 10 to over 1 : 1000'. What is a 'gem'? Karanth begins the book by providing a reasonably clear answer in the introductory chapter and has assembled in the remaining eleven chapters, the vast amount of scientific knowledge on gems, employing an elegant approach. Over 240 and odd gems known to mankind are listed along with their important physical properties in the 'gem index' (Appendix-1). 1 feel that perusing this gem directory first may be a better way to start reading the book. Only a specialist can point out whether there are significant omissions in the gem index! Chapters contain detailed description of the characteristics, their occurrences in India, etc. by classifying them into isotropic (ch 9), uniaxial (ch 10), biaxial (ch 11) and organic and miscellaneous gems (ch 12). In my opinion, these nine chapters along with Appendix-1 form the core of the book (say. Part 1). The other three chapters are devoted to gem industry in India (ch 2), synthetic gems (ch 7) and gem cutting (ch 8). They could well have been shifted after the above-mentioned nine chapters, to retain the development and flow of the main theme (and called Parts II and III). There are 48 beautiful colour photographs (60 mm x 50 mm size) and one of them, the cut forms of crystalline silica, adorns the dust jacket of the book. The bibliography has over 180 references for further reading.