106 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
The above tabulation presents clearly to the eye the distinctive features of 
these five volcanic minerals, which are arranged therein in the order of their 
content of silica; and as no such extended research into the composition of these 
minerals has before been published, it is necessary, in the first place, to consider 
the formula of each. 
This in the following tables is done by giving in the first column the 
average composition. This is followed by the calculation of atoms—the last 
column giving the percentages calculated from the formule which stand 
below :— 
Delessite. 
Atoms. 
Silica, : | oi 26 1°041 =a) 3 ole 
Alumina, . se LOG 302 ) 1 1 16°28 
Ferric Oxide, . 2°32 0295 258 
Ferrous Oxide, . 12°96 * 36 \ 3 4 1261 
Magnesia,. . 21°22 1:061 ; 71:02 
Water, . a» 14 52 1°614 4°9 5 15°76 
Formula— 
(Fe! Mg?) Si? + (Al,* Fe,*) Si + 3H, + 2MgH,. 
Or generally— 
(R? R,) Si? + 3H, + 2MgH, . 
Or atoms— 
R4, Ry1, Si 3,1, 6; 
Chloropheite. 
Atoms, 
é es) 3 12 i 2 ped 36° 24 
Alumina, . . 10°54 * 205 \ 35 1: 8°87 
Ferric Oxide, . 12:04 i) 13°81 
Ferrous Oxide, . 2°04 ‘057 Da? 
Lime, : ee ae) 5} if 2° a8 
Magnesia, . 10% °5 10°01 
Water, . ) nee 2°87 2°87 fi 24°85 
Formula not evident. 
Atoms— 
R4,R,2,Si7, H,16. 
