106 
NATURAL HISTORY. 
[long 
mens of rock crystal in a wrought state are added, among 
which is Dr. Dee’s show-stone (see Walter Scott’s Demon¬ 
ology), &c. 
Case 21. Common quartz: among the specimens of this 
widely diffused substance, which offers such great variety 
in its external aspect, the more remarkable are the hacked, 
corroded, and cellular quartz from Schemnitz, as also the 
pseudomorphous or supposititious crystals, principally 
derived from modifications of calcareous and fluor spars; 
and, with regard to colour, the blue quartz, called siderite, 
from Salzburg, and the rose or milk quartz , which are both 
used as ornamental stones ;—- fibrous quartz ;—flexible 
sandstone from Brazil; —iron flint. In this Case are also 
deposited several varieties of stalagmitic quartz or quartz- 
sinter, the most remarkable among which are the siliceous 
concretions deposited by the celebrated hot spring in Ice¬ 
land, the Geyser; another variety of it is the pearl-sinter 
from Santa-Fiora in Tuscany (whence it has obtained the 
name of Jiorite ), and from the island of Ischia. With 
these are placed specimens of the ceraunian sinter or those 
enigmatical siliceous tubes which were discovered in the 
sands of the Senner Heath in the county of Lippe (where, 
on account of their supposed origin, they are called light¬ 
ning tubes, from which name those of fulgurite, ceraunian 
sinter, astraphyalite, are derived), at Drigg on the coast 
of Cumberland, and latterly, by the late Capt. Clapperton, 
near Dibbla in the Tuarick country, Africa, from which 
localities specimens are here deposited. The hyalite is 
placed here as a mineral related both to stalagmitic quartz 
and calcedony.— Haytorite. 
Case 22 contains some more of the varieties of common 
quartz : prase, which appears to be an intimate mixture of 
this substance and actinote ;—the avanturino quartz as 
also some varieties of the cat's eye (mostly from Ceylon), 
in which the chatoyant lustre is generally produced by 
nearly invisible fibres of amianth lodged in the quartzy 
mass.—Part of this Case is occupied by the siliceous sub¬ 
stance called hornstone, divided into the conchoidal and 
splintery varieties; among these are the remarkable pseu¬ 
domorphous crystals from Schneeberg in Saxony, derived 
from various modifications of calcareous spar; also beauti¬ 
ful spec mens of wood converted into hornstone, being the 
