COLLECTION OF MINERALS. 291 



under the name of quartz, we see one of the 

 most abundant species in nature, and the modi- 

 fications of which are the most numerous and 

 diversified. We will examine this substance in 

 its purest state, the whole of whose varieties 

 bear the name of hyaline quartz. The first is trans- 

 parent and crystallized, and is known by the 

 name of rock-crystal. There are some beautiful 

 specimens on the shelves of this and the adjoin- 

 ing cases. The most general form of these crys- 

 tals is a solid of six sides, terminated with two 

 pyramids with six faces. The Museum possesses 

 a fragment of such a crystal, the enormous size 

 of which prevented its being placed in this gal- 

 lery : it was brought from Valais, and weighs 

 more than 800 pounds. It has been placed on 

 the staircase, leading into the first geological 

 room. A group of similar crystals of a remark- 

 able size is placed in this room, near the win- 

 dows; the crystals are nearly a foot long, and 

 altogether weigh 325 pounds : they come from 

 Fischbach, in Valais. The colourless hyaline 

 quartz, or rock-crystal, is employed in making 

 lustres, vases of different forms, etc. 



This substance is not always limpid, as in tlie 

 crystals of which we have just now spoken ; it 

 is often coloured by other matter, without en- 

 tirely losing its transparency, and then it is named 



'9- 



