416 SKY. MINERALS. 



quarry of Strath, portions of a calcareous, steatitical, and 

 white laminar matter, are found highly coloured by the 

 red oxide of manganese, forming a mineral of considerable 

 beauty. 



In the same place occurs a peculiar quartz deserving 

 description. This forms distinct masses imbedded in the 

 marble, appearing solid in the centre but exfoliating near 

 the surface in crusts, a white steatitical earth being occa- 

 sionally interposed. Some portions are finely granular, 

 and the whole is of a snowy whiteness. The most re- 

 markable circumstance is its extreme tenderness when 

 first taken from the quarry. Hence the purer parts 

 crumble into sand under the fingers, while those which 

 contain the steatite can be wrought into a tenacious paste. 

 In a few days the whole acquires the usual hardness of 

 similar substances, and the quartz becomes an ordinary 

 granular and saccharine quartz. I have on different occa- 

 sions mentioned this fact, but this is the first instance in 

 which I had noticed it in quartz. 



In the circumstances under which fresh specimens are 

 usually collected it rarely happens that an opportunity 

 is afforded for ascertaining by experiment the quantity 

 of water that in such cases is contained in rocks or 

 minerals, the loss being generally rapid and the fact past 

 investigation before it is possible to weigh them with the 

 requisite care. I cannot therefore pretend to state the 

 proportion of water contained in this quartz, but I have 

 in other situations of greater convenience made the requi- 

 site trial on various substances, and always found that 

 proportion remarkable. In the argillaceous rocks, or in 

 rocks of a lax texture, it may be imagined that the water 

 is simply contained among the interstices, although the 

 loss of it would even then scarcely explain the great 

 change of hardness they undergo on drying.* It is un- 



* A very remarkable example of this circumstance sometimes occurs 

 in those veins which occasionally traverse granite, and are well known 

 from presenting the mixed aspect of a fine grained granite and an argil- 



