TEIP TO MADAGASCAR — LACROIX. 379 



The beryl is common enough.^ It is of a pale rose or dark carmine 

 color, so unusual that it is proposed to give to it a s})ecial name, that 

 of "morganite." 



Spodumene,^ almost everywhere else epaque, is found in a limpid 

 form, of a beautiful rose color with a tinge of lilac, accompanied by 

 an exceptional brilliancy, and this variety, the "kmizite," forms a 

 magnificent stone, rivaling the one which until then had been found 

 only in California. 



However, I must mention a garnet,^ the spessartite, supplyuig some 

 orange-colored gems having a refraction as odd as it is strong, besides 

 a mineral makmg, also, its first appearance as a precious stone, the 

 danburite,'' which, once cut, is hard to distinguish from the yellow 

 topaz of Brazil. 



Often inclosed in pegmatite and without distinct crystal forms, all 

 these muierals, with many others besides,^ show themselves in pockets 

 of crystals, a description of which would not be out of place hi a tale 

 of the ''Thousand and One Nights"; tmy grottos with marvelous 

 walls illumined by the sparkling of thousands of crystals, and among 

 them one does not know what to admire the most, the delicateness 

 and perfection of the forms, the multiplicity and brilliancy of the 

 faces, or the variety and richness of the colors. 



While they may form, like the aquamarine, some prisms of gxeat 

 dimensions, or even the smallest crystals, but with faces of a won- 

 derful clearness, like those from the pockets, or agam some shapeless 

 fragments, all the transparent minerals taken from the open quar- 

 ries * are carried each evening to the foreman, called the commander, 



1 The beryl of Madagascar does not always have the simple composition (silicate of alumina and glucina) 

 that has long been attributed to it; very frequently, above all in the lithia-bearing pegmatites, part of the 

 glucina is replaced by some alkalies, of molecular weights more or less considerable (lithium, rubidium, 

 cae~sium), and this substitution at once prevents the increase of density and that of the indices of refrac- 

 tion. This variation is continuous; ic is not necessarily connected with the color, but the light beryls are 

 most often blue or green, the heavy ones more often rose. 



A knowledge of this property is very important in order to diagnose these precious stones, the density 

 of which may vary from 2.70 to 2.9n and the indices in the following limits: 7?;;=1.5S1,S to 1.6021, «p=1.5756 

 to 1.5953, in the specimens studied up to the present time, and which does not constitute, perhaps, the 

 extremes of that series. I should add in addition to this that the very dense beryls, instead of being 

 lengthened near the vertical axis, as in the very light ones, are flattened near the base. I have discussed 

 that question recently in the Bulletin de la Soci6t6 frangaise de min^ralogie, volume 31, 1912, page 200, 

 and in some previous articles. 



2 This mineral belongs to the pyroxene group, of which it shows the crystals; it is a silicate of alumina 

 and lithia. 



3 The spessartite is an alumina and manganese garnet, containing a little lime; that orange color is special 

 to Madagascar; it can be compared, but it is not identical with the spessartite of Xorth Carolina. In the 

 aquamarine beryl pegmatites some garnet is also found, but it is the almandine, red and opaque. 



■" This mineral Ls a silico-borate of lime; I announced its existence in Madagascar (Bull, Soc. fran^. min6r., 

 vol. 31, 1908, p. 314), from some crystals from the valley of the Sahatany. 



* We should also mention among the minerals found in pegmatite apatite, rhodizite, and blomstran- 

 dite; as to crystalized minerals from pockets, they are quartz, microdine, albilc, tourmaline, beryl, and 

 lepidolite, to which we should add two new mineral species that I have called " bityite" (Comptes Rendus, 

 vol. 141), 190S, p. 13C7) and the "manandonite" (Bull. Soc. frang. miner., vol. 35, 1912). 



' In a few deposits the pegmatite is found intact and very hard. More often it is either kaolinized or 

 lateritized, and in these two cases it has become soft enough to bo quarried with the pickax or shovel; the 

 gems can then be easily extracted. In many of the beds they work on ^luvions, collecting the pegmatite 

 in placeorfallen to its immediate vicinity. 



