M. Delesse on Globuliferous Rocks. . 
them more or less thickly in globules.* These globules are 
generally ens and this memoir has especial reference to 
th ind, occurring in rocks that are rich in silica. 
Gestiaen are sometimes globuliferous, as those of Rappawiki, 
in Finland, which contain globules consisting’of orthoclase, sur- 
rounded by oligoclase. But these researches relate particularly 
to porphyritic or compact rocks, especially eurite, pyromeride, 
trachyte, retinite, perlite, obsidian, and a large variety of por- 
phyries. The pyromerides of Corsica and the Vosges, the 
porphyries of Esterel, of the country of. Bade and Thuringia, 
the trachytes of Iceland, the retinites of Saxony, and the perlites 
and obsidians of Hungary, are taken as types of this structure. 
The globules vary much in color, being either black, violet, 
green, brown, yellowish, reddish, gray or white ; usually differing 
alittle from the color of the paste. ‘They are commonly harder 
than feldspar, when undecomposed, owing probably to the excess 
of silica; but in perlites they are less hard than feldspar, perhaps 
because the mineral is in a semi-vitreous state, and also, it may 
be, because opal penetrates them, as stated by Hausmann aud 
Fuchs. The specific gravity is low, viz. 23-26; 2-322°4, 
perlite. This.is. far less than for quartz, which has G. = 2.65. 
Before the blowpipe, they fuse less easily than feldspars, owing 
to the excess of silica and small proportion of alkalies. 
Composition :-— 
ae Si Al #e Mn Ga Mg Nak. ign 
1. Fr. Pyromeride, Wisenheim, 88°09 Hie 0- 58 —- 0°28 1°65 2°53 «084 =100, Delesse. 
2 Fr. Pd Hlinic Ks Hung., 43 - 12°00 2°45 1] oa3 1'76=1 , Ficinus. 
3. Fr. e; Baula 58 43-78 1-04 4 1°19 O85 068 B57 263 208— 101-00, Forchh. i 
= - ttn Baxony, 3. 00 14:50 1-00 0-10 1-00 1-75. 8°50 99°85, “Klaproth. 
Perlite, Saxony, 68°53 11-00 4:00 2:30 8-33 1°20 3-40 0:30 —99°16, Erdmann. 
Phe large excess of silica is the remarkable characteristic, and 
as a general rule in the pyroméride, the composition of the 
globules is the inverse of that of the enveloping rock, 
Structure—The globules have generally a well defined 
structure. In most of the pyromerides of Corsica and the oe 
4, Recherches sur l Association des Mineraux dans og» 
pouvoir magnétique élevé-—Bull. de la Soc. Geol. — aca (3) vii, oF ton ra 
15. Sur la Variolite de la Story ce—Ann. des Mines, (th 6 116, 1850. 
i énite Rose d’ 
Bull. Soe. Geol. de France, vii, 484, 524, 1 
. 17, Sur le gies de vm [2h et de Samat ne —Bull. Soe Geol. de 
a [2], vii, 310, 1 
| ur la Constitution Minéralogique du Diorite, Kersantites—Ann. des Mines, 
it 149. 
ur la onsttt ution rrr it de la Calcaire Saccharoide du Gneiss. 
yh, des Mines, xx, 141, 
_* This sub ject has’ a apd hy revive ed some attention—see especially, von Bucu, 
Recueil de planches de Petrifieat fons remarquables, fol.; R. C. vox Leonsarp, 
Charakteristik dr Fist Ba. 52 L. Bronenrart, Essai ar les Orbicule es siliceuz, 
a the hack der Geognosie 
