70 THOMAS STEERY HUNT ON A NATURAL SYSTEM IN 



elaborate chemical studies of Rammelsberg, when properly interpreted, will throw much 

 light on the coustitution of the micas.' For greater simplicity the water-ratios, which 

 are given in Table IX, are here omitted. 



§ 91. Eelated to the chlorites, but dilFeriug in structure, is the epichlorite of Kam- 

 melsberg, described as iibrous or columnar, and having the atomic ratios, 4:3:9:4, 

 which corresponds to a more siliceous prochlorite. In this connection may be mentioned 

 a hitherto uudescribed mineral which is found in veins in the anthracite and its accom- 

 panying carbonaceous shales at Portsmouth, Rhode Island. This substance is sometimes 

 found penetrating quartz, but in its pure state appears as a greyish green mass, consisting 

 of fine flexible fibres resembling chrysotile or amianthus, with which it has been con- 

 founded. A portion from a vein about an eighth of an inch wide gave me by analysis : 

 silica, 2Y.80 ; alumina, 21.80 ; ferrous oxyd, 26.10 ; magnesia, 8. 90 ; lime, 2.01 ; potash, 2.69 ; 

 soda, 4.24; volatile, 9.30 = 102.90. A subsequent microscopic examination of the material 

 analyzed showed the presence therein of interspersed films of pyrites, thereby vitiating to 

 some extent the results of the analysis, which deserves to be repeated on a portion of the 

 mineral purified by the aid of bromine-water. Making allowance for some pyrites, the 

 atomic ratios of this fibrous species are 4:4:6:3, being near to prochlorite and to voigtite 

 which like it contains a little lime and soda. In this unnamed amianthoid mineral from 

 Portsmouth, possessing nearly the composition of a chlorite or a hydrous biotite, and in 

 the epichlorite of Rammelsberg, we have apparently examples of a hydrospathoid form of 

 these alumino-maguesian protopersilicates. 



With these should be noted the pilolite of Heddle, who has described under that 

 name the substances hitherto known as mountain cork and mountain leather, which have 

 a fibrous texture, are more or less flexible and tough, and occur in veins or fissures alike in 

 crystalline limestone, in sandstones and shales, and also, as observed by the writer, as a 

 deposit upon quartz crystals in granitic veins. From several analyses by Heddle, pilolite 

 is shown to be a highly hydrated silicate of alumina and magnesia with ferrous oxyd, and 

 is nearly represented by (mg2..-,fe„.-,aLsiij)Oa,+ 12aq, a formula requiring silica, SVl; alumina, 

 VB ; magnesia, 115; ferrous oxyd, 6'2; water, 248 = lOO'O. More than one third of the 

 combined water is expelled at a temperature of 100° centigrade." 



Tribe 10. — Pinitoids. 



§ 92. Corresponding with the ophitoids of the protosilicates, we find in the present 

 suborder a tribe of hydrous silicates which, since the species known as pinite may be 

 taken as the type, Ave have called Pinitoids. These bodies approach in composition and in 

 density the hydrous muscovitic micas, with compact varieties of which they may be 

 confounded. The true pinitoids, however, appear to be amorphous colloidal silicates like 

 serpentine ; w^hile pinite itself with its A^arieties, which have been described under the 

 various names of gieseckite, agalmatolite, dysyntribite and parophite, though generally 

 amorphous, seems in some cases, like the serpentinic silicate, to be crystalline. We have 



' I have to acknowledge my indebtedness in very many cases to tlie First Ajipendix to Dana's jMineralogy 

 by Brush in 1872, and to the Second and Third Appendiices by E. S. Pana, in 1875 and 1882. 

 - Mineralogy Mag., 187(1, ii. 20(i, cited in the Third Appendix to Dana's ISIineralogy, p. 94. 



