Washington and Wright — Feldspar from Linosa. 61 



From the above data on the percentage composition in terms 

 of the different mineral molecules (Or, Ab, An, JSTe), the 

 specific gravity of the mineral can be calculated on the assump- 

 tion that no great volume change in the component molecules 

 has taken place, a condition which experience has shown to 

 hold true for practically all cases of solid solution. The weight 

 per cent of each molecule present, divided by its density in 

 crystallized condition, furnishes its specific volume or its 

 volume compared with Avater of equal weight. The sum of 

 these specific volume values for all the molecules present 

 denotes in turn the specific volume of the substance, the 

 reciprocal of which is the density required. In this calculation 

 the most accurate density determinations of the components 

 were used, namely : Or = 2*55, Ab = 2*605, An = 2*765, and 

 Xe = 2*571 (the last determined on artificial triclinic JSTa 2 Al 2 - 

 Si 2 8 ). The resulting density, 2*685, approximates very closely 

 the measured density, 2*693, and is almost identical with this 

 as corrected for the magnetite inclusions, 2*684. This in itself 

 is a strong proof that the Linosa mineral is a mixed crystal of 

 feldspar and soda anorthite. 



This complex mineral would belong logically to the group 

 of feldspars, just as do the barium-bearing members of the 

 orthoclase-celsian series, some intermediate members of which 

 are called hyalophane, and which contain the molecule 

 BaAl 2 Si.,0 8 . In this connection it is interesting to note that 

 a sodium-barium plagioclase, described by Des Cloiseaux,* was 

 crystallographically similar to albite-oligoclase, optically like a 

 labradorite, and with the oxygen ratios of andesine. Mention- 

 ing this mineral, Rosenbuschf points out that, as celsian is 

 monoclinic, the barium alumino-silicate must be. dimorphous. 



The Linosa mineral would thus be a representative of a dis- 

 tinct and hitherto unrecognized triclinic feldspar series, char- 

 acterized by the joint presence of molecules of albite, lime 

 anorthite, and soda anorthite. Reckoning in with the soda 

 the small amount of potash present, and distinguishing the 

 lime and soda anorthites as Can and Nan respectively, our 

 feldspar would have the composition AbgCan^Nan^ 



Regarded as a feldspar of such abnormal character, and 

 especially if the assumption is verified that soda anorthite is 

 present and that we are dealing with a representative of a new 

 feldspar series, the Linosa mineral is deserving of a new name. 

 For this we propose anemousite, after the ancient Greek name 

 of the island. The term anemousite would imply, of course, 

 not only a feldspar with the exact composition given above, 

 but, like hyalophane, oligoclase, labradorite, etc., could be 



*Tschenn. Min. Mitth., p. 99, 1877. 

 fMikr. Phys., vol. i, part ii, p. 313, 1905. 



