gallery.] natural history. (Minerals.) 65 
distinct species, are mostly indebted for their generally very striking 
external characters to the admixture of matter foreign to the species, 
or to other casual circumstances that prevailed at their formation. 
Case 20. Amethyst quartz of various tints, in grouped crystals, &c. 
Hock crystal: various modifications of crystalline forms : small 
dodecahedral and other crystals, known by the names of Gibraltar 
diamonds, Bristol diamonds, &c. ; varieties of colour, according to 
which this substance obtains the familiar denominations of smoky topaz 
or morion, cairngorm, citrine, &c. ; specimens of rock crystal enclosing 
various substances, such as rutile, brown iron-stone, micaceous iron, 
acicular antimony, actinote, asbest, chlorite, &c. ; groups of rock 
crystal ; some specimens of rock crystal in a wrought state are added, 
among which is Dr. Dee’s show-stone (see Walter Scott’s Demono- 
logy), &c. 
Case 21. Common quartz : among the specimens of this widely 
diffused substance, which offers such a 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 iluor 
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 ( itacolumite ) from Brazil*, 
China and the East Indies -fetid quartz , from Nantes iron-flint. 
In this Case are also deposited several varieties of stalagmitic quartz 
or quartz- sinter, the most remarkable among which are the siliceous con- 
cretions deposited by the celebrated hot spring in Iceland, the Geyser ; 
another variety of it is the pearl-sinter from Santa- Fiora in Tuscany 
(whence it has obtained the name of fiorite ), 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 
probable origin, they are called blitz-rohren, or lightning tubes, from 
which name those of fulgurite , ceraunian sinter , astraphyalite, are de- 
rived), at Drigg on the coast of Cumberland, and lastly, by the late 
Capt. Clapperton, (see Append, to his Journal,) near Dibbla in the 
Tuarick country, Africa, from which localities specimens are here 
deposited. The hyalite is placed here as a mineral related equally to 
stalagmitic quartz and opal; — the haytorite , a pseudomorphous sub- 
stance, being purely siliceous, but presenting the form of datolite ; — 
the avanturino quartz. 
Case 22 contains some more of the varieties of common quartz ; 
prase , which appears to be an intimate mixture of that substance and 
actinote ; — as also some varieties of the cat's eye (mostly from Cey- 
lon), 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 substance called hornstone , divided 
into the conchoidal and splintery varieties ; among these are the re- 
markable pseudomorphous crystals from Schneeberg in Saxony, derived 
* Large specimens of flexible sandstone are placed in a table in the m iddle of the 
room, opposite Case 21: they are from the mountains of Itacolumi, near Villa 
Ricca, in Brazil, and were presented by His Excellency Viscount Strangford. 
