A NATURAL SYSTEM IN MINERALOGY. 67 
external characters of colloidal or porodic substances, are placed in the colloid tribes; to 
which, in the synoptical tables, we have added sordavalite and hisingerite, the latter 
being regarded as a simple ferric silicate, and thus in the third sub-order. 
For the colloids included under the tenth tribe, the very variable composition of the 
vitreous products of igneous fusion has been insisted upon in § 103, 104 of the previous 
paper. 
TaBze II]. — ProTapAMANTOIDS, 


As regards the limits of species in these and similar cases, the question which 





<= 
SPECIES. Formua. 12 | 40) | V | x 
Chondrodite. - - |(mgysi,)jo, - - - - - - 18.64 | 3.20] 5.82) O. 
Monticellite. - - | (m,si,)o, - (m= mgp.;Cao.5) - 19.50 | 3.25] 6.00) O. 
Forsterite. - ~-|(mgsi,)o,- - - = - - = 17.50 | 3.30] 5.30} O. 
Chrysolite (1). - | (m,8i,)0, - (Mm = mgp.ofe., - 18.30 | 3.40] 5.38] O. 
Chrysolite (2). - | (mjsi,)o,-(m—=mgy.,fe,. - 19.10 | 3.50) 5.45) O. 
Bertrandite. - - |(glisi;)o, +}aq - - - - - 13.22 | 2.59] 5.10) O. 
Phenacite. - -|(glisio, - - - - - - - 15.75 |3.00) 4.58} R. 
Amphibole (1). - | (msi,)o, - (m — mg, Cay.95) 17.33 | 2.97| 5.88) C. 
Amphibole (2). - | (mysi,)o, - (M = M¥p.gCApegfCp-1) 18.00 | 3.06] 5.88] C. 
Rhodonite. - -|(mmjsi,)o, - - - - - - 21.83 | 3.60} 6.06) C. 
Pyroxene (1). - | (Mm Si,)o, - (m = cay.;mgp.;) - 18.00 | 3.27] 5.50) C. 
Pyroxene (2). - | (m,si,)o, - (m= cay.;mMgp.5) - 18.00 | 3.28] 5.48} C. 
Pyroxene (3). - | (mySi,)o; - (m= cakmg#) - 17.55 | 3.22) 5.45) C. 
Pyroxene (4). - (m,si,)o, - (m = catmg?feh) 18.66 | 3.41| 5.47] C. 
Enstatite (1). - | (m,si,)og - (m = mgyfey,) - - | 17-20 [8.10] 5.54) O. 
Enstatite (2). - | (mysi,)o, - (m= mgp.gfeg.y) - 17.73 | 8.25) 5.45) O. 
Titanite. - - -|(ca,si,tiJo, = - - - - - - | 19.80 |3.50/5.65| C. 
Guarinite.- - - | (casi,ti,)o; - - - - - - 19.80 | 3.50) 5.65) T. 
Danburite. - - | (caysijb;)o3 - - - - - - 15.37 | 3.00 5.12) O. 





arises is similar to that presented by the various intermediate feldspars and scapolites, 
(which we have elsewhere discussed), and by the intermediate carbon-spars, and is one in- 
timately connected with the high molecular weights which must be assigned to mineral 
species. 
Taste IV.— PROTOPHYLLOIDS. 






| SPECIES. FORMULA. | P D | V X. 
| Thermophyllite. |(mg;si,)o, + 2aq -|15-33 | 2-61 | 5-87| ? 
| Marmolite. - - |(mg,si,)o, +2aq -| 15°33} 2-41 | 6-35| ? 
Tale. - "| (mesi)ontlaq -| 15°93 | 2°70 || 5:90) O: 
Tale - - - - |(mgssi)o, + $aq -| 15°82 | 2:60 | 6-07] O. | 

§ 7. In the chemical relations of the protoxyds on the one hand, and of alumina on 
the other, upon which, in our system, the sub-orders of silicates are based, a fundamental 
difference appears in the fact that when silicated compounds of the former undergo sub- 
aerial decay—that is to say, are decomposed by the action of carbonated atmospheric 
