
318 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
The average composition of these garnets, excluding the Garve specimen, is 
as follows :— 
Oxygen. 
Silica, . ; - 36°14 19°27 19-27 
Alumina, en 18°05 ye 11°12 
Ferric Oxide, 5 9°04. 2°44. 
Ferrous Oxide, . 21°35 4°74 19°54 
Manganous Oxide, 13°69 3°09 
Lime, . ; ; OTT “227 Sea2)) 
Magnesia, . ; °55 22 
Water, : : °16 5s 
The alumina is to the ferric oxide as 3 to 1; the ferrous oxide’to the man- 
ganous oxide as 3 to 2. Though the protoxides do not here balance the sesque- 
oxides well,* the formula may be stated generally thus— 
(Fe*’Mn?)Si’ + (Al,’Fe,)?Siz , 
and no garnet yielding even approximatively such a proportion of manganese 
has before been noticed. The manganese is doubtless the cause of the lively — 
colour. : 
This may be called a manganesious garnet, in contradistinction to the true 
manganesian garnet, found in America, Miask, and elsewhere, and of which 
the formula is—(Fe, Mn’)?Si? + Alsi 















S. G. Si. ‘Alp. Feo, Fe. Mn, Ca. Mg. H,0. Total. 
Grossular— 
Creag Mohr, P . | 3°545 || 39°83 | 9°74 | 15°07 ay "35 | 33°57 | 1°01] °05 99°73 
Cinnamonstone— 
Glen Gairn, ‘ A Sy 39°27 | 21°98} 1°49] 3°93 *33 | 31°88 6 18 99°66 |. 
Pyrope— ; 
Elie, , A A . | 4°124 || 40°92 | 22°45 | 5:46) 8:11 46] 5°04/}17°85| ‘1 100°39 
Common Garnet— 
Burra Voe, Yell, . . | 3°997 || 87°3 | 21-1 7°47 | 24°02) 2°14|) 4°43) 3°53]... 99°98 
Killiecrankie, , ; | 35688 || 37-59) 13°66), 3566) 32°31 14247 1) 4-12) 3-467) 82 99°59 
Meall Luidh, ; eal) ee 3h | 148 A DON S2°90 | 28h) sOrs9)|) LeSili|) see 100°05 
Knock Hill, : resales eyeeal | es) | les eee GET abn el VARI) 100°85 
Almandite— 
Clach an Edin, . rile sed 39°93 | 19°81 | 13°69 | 13:29 | 1° 9°13} 3°31] ... 100°15 
Precious Garnet— 
Glen Skiag (red), . | 4°125 |] 85°99 | 16:22 | 8°64 | 23°27 | 15°24 “4 “47 | °25 100°48 
Do., do. (brown), ce ae 36°08 | 18°96 | 7:03 | 21°56 | 13°62] 1°77 9 33 100°29 
Loch Garve, é . | 4°122 |) 86°15 | 21°94 1 15°15 | 15°09 | 7°85} 2°07) 1°62) “31 100°16 
Struay Bridge, Sul Seep 35°66 | 15°8 | 13°12 | 22°21) 11°43] 1:12] ... 06 99°39 
Ben Resipol, : A eee 36°85 | 21°24] 7°38 | 18°38 | 14°46 ‘78 8D) ces 99°92 






* This possibly may, in one or two of the specimens, be from the decomposition with the fluor 
spar and sulphuric acid not having been absolutely perfect. |My assistant conceives that a mixture of 
potassium fluoride with fluor spar is, from the greater energy of the reaction and the smaller quantity 
of resultant calcium sulphate, to be preferred. The greater energy of the reaction, however, entails a 
certain amount of risk of projection from the crucible. It is much to be desired that pure ammonium 
fluoride could be procured, 
