226 " Larsen and Glenn — Minerals of the 



nating mole cnla rly. Copper-zinc melanterite would have 

 Cu predominating molecularly. To be precise, for zinc 

 melanterite the molecular ratio ZnO to CuO should be 

 greater than 3 to 1, for zinc-copper melanterite that ratio 

 should be between 3 to 1 and 1 to 1, for copper-zinc melan- 

 terite between 1 to 1 and 1 to 3, and for copper melanterite 

 the ratio should be less than 1 to 3. Similarly the chal- 

 canthites are minerals with the general composition 

 RO.S0 3 .5H 2 0, they are triclinic and their properties are 

 related to those of the common mineral chalcanthite. In 

 both groups the various members are similar in all their 

 physical properties, notably in their optical properties. 



If the unsystematic procedure of giving each species a 

 distinct name without regard to its relations to other min- 

 erals had been followed out in the present paper six new 

 mineral names would be required for six relatively unim- 

 portant minerals and it is probable that in both groups 

 there are many more members. If independent names 

 are given to all the members of both groups very few min- 

 eralogists would find it worth the effort to remember the 

 significance of the various names, but if Washington's 

 suggestion, or some modification of it, is carried out for 

 the groups every mineralogist should know the composi- 

 tion and group relations of any member from its name. 

 It is sincerely to be hoped that mineralogists will soon 

 adopt a systematic nomenclature. 



Physical properties. — Zinc-copper melanterite is pale 

 greenish-blue (calamine blue 43d of Eidgways 3 color 

 standards). It has a vitreous luster, a hardness of about 

 2, and a specific gravity as determined by matching in a 

 heavy solution of 2.02. It fuses readily with intumescence 

 at about 1 to a white froth which on high heating turns 

 black; on rapid heating it decrepitates violently. It 

 colors the flame green. It loses water in a dry room as 

 will be shown in a succeeding paragraph. It is readily 

 soluble in water. 



Under the microscope it is seen to consist of very pale 

 blue-green rods not sensibly pleochroic and nearly a milli- 

 meter across and several millimeters long. The indices 

 of refraction were measured by matching in oils and 

 immediately measuring the indices of refraction of the 

 oils, and the following values should not be in error more 

 than 0.001 ; a = 1.479, p = 1.483, y = 1.488. The mineral 



3 Bidgeway, Eobert. Color Standards and Nomenclature, 1912. 



