378 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



In several deposits situated outside the Sahantany ^ region there 

 is also found an abundance of monazite, a cerium phosphate sought 

 for on account of the small quantity of thorium which it contains, 

 thorium entering into the composition of gas mantles used for inten- 

 sive lighting. One can find there also some uranium bearing titano- 

 tantaloniobates ^ from which the precious radium is extracted. 



It is not rash to think the day is not far distant when these minerals 

 will no longer be mere scientific curiosities, but will become material 

 profitably turned to account. 



The second group of pegmatites is characterized by a greater 

 variety of gems.^ The most abundant is tourmaline. This sub- 

 stance furnishes with beryl and corundum an illustration of the fact 

 that the color of minerals does not generally constitute one of their 

 essential characteristics. One can not conceive of malachite other 

 than green, but very rare are the minerals which, like that, have a 

 color which belongs to them alone. The coloration of nearly all spe- 

 cies of minerals, and particularly some precious stones, is only a 

 natural tint, existing ordinarily in such a small proportion that in 

 many cases one may still dispute its nature. 



In the Sahatany region the transparent tourmalines are the most 

 beautiful gems, running all the possible gamut of colors. Rarely 

 colorless, they are red and of many different reds; pigeon blood like 

 the beautiful ruby, reds more or less tinged with violet, fading away 

 to the most delicate rose; there are some greens and blues, some 

 browns with now and then a smoky tint, some golden yellows, and 

 one of dazzling gold. Here the colors are uniform in the same 

 crystal, there they alternate to form harmonious blendings,^ 



By the side of these transparent stones are also found, as in the 

 preceding pegmatites, a black tourmaline of no possible use.* 

 Though from a reminiscense of the war of conquest in which the 

 Senegal sharpshooters played a r61e that the Malagasys have not 

 forgotten, they call these stones " Senegal." 



1 The deposits where this mineral exists in great abundance and La large crystals are to the north of Betafo 

 (Ampangab^, Ambatofotsikely, etc.); it is there accompanied by ampangabeite, colnmbite, striiverite, 

 and some bismuth minerals. (A. Lacroix, Bull. Soc. frang. min^r., vol. 34, p. 63, and vol. 35, 1912, p. 76.) 



2 1 have distinguished two groups among these minerals. (Comptes llcndus, vol. 144, 1912, p. 797, and 

 Bull. Soc. franp, min<5r., vol. 31, 1908, pp. 218-312; vol. 33, 1910, p. 321; vol. 35, 1912, p. 84.) The first is 

 isometric and comprises blomstrandite and two new species that I have called betafite and samiresite; 

 these minerals crystalize in great yellow or greenish octahedrons; the second is orthorhombic and includes 

 eux^nite, samarskite, and the new mineral that I have named ampangabt5ite. We must add to it the 

 tetragonal fergusonite. 



3 The mineralogical characteristics of these pegmatites are its abundance of sodium and lithium bearing 

 minerals; when mica exists it is no longer potash-mica, but lepidolite and zinwaldite rich in lithia. B iotite 

 is common to two types of pegmatite, of which I have recently stated the diflerentcharacteristics. (Comptes 

 Rendus, vol. 155, 1912, p. 441.) 



« I have given in my Min6ralogie de la France et de ses Colonics (vol. 4, p. 695) a detailed study, accom- 

 panied by numerous photographs, of these blcndings of various colors, submitted with some interesting 

 models in harmony with the ternary symmetry and occasionally with the hemimorphisms of the mineral 



» In the pegmatites with the blue beryl these tourmaline crystals are sometimes of colossal dimensions 

 (more than a meter). 



