10 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
MARGARODITE. 
From Gneissose Rocks. 
1. From a stratum of kaolin which occurs at Mouwick, Lambhoga, Fetlar, 
Shetland. 
Kaolin is not found in many localities in Shetland, but when found it 
occurs in considerable quantities. Mouwick and Grunies’ Geo in Fetlar, the 
burn of Tractagill, and the trough which runs north from Weesdale Hill are the 
chief localities. It has been in these islands used as a Fuller’s-earth, and for 
white-washing houses. In all of the above localities it has a glistening appear- 
ance, which seems in all to be due to its containing, like that found at Mouwick, 
a quantity of minute scales of margarodite. Of this the kaolin of Mouwick 
yields to elutriative processes about one-fifth part. This margarodite has a faint 
yellow colour, a pearly lustre, and is very unctuous to the touch. It may by 
continued friction be reduced to very minute scales, but not to an absolutely 
impalpable powder like talc ; this is a physical mode of discrimination between 
these minerals. 
1-302 grammes of this margarodite yielded— 
Silica, ; : : °655 
From Alumina, ‘ -006 
"6600 "== “0 468 
Alumina, . : ‘ SEB AL CHAIe 
Ferric Oxide, . ; a dca Lis, 
Manganous Oxide, . ; “23 
Lime, ; ; : : "946 
Magnesia, "786 
Potash, . ; eer ait 
Soda, : : "io 
Water, . ; J M969 
99-347 
It absorbs «89 per cent. of water. 
The “kaolin” also contains a quantity of grains of angular quartz. 
2. From Vanleep, Hillswick, Shetland. Occurs, associated with reddish 
coloured kyanite, in the quartz veins of a very micaceous gneiss; it is imbedded 
along with ripidolite (?) in crystals, or crystalline plates, among the interlacing 
crystals of the kyanite 
Colour almost white, sometimes very pale greenish: lustre very high 
pearly, almost equal to tale. 
