34 
On the Minerals of the 
[Feb. 
striking fire copiously with steel, with a large conchoidal fracture, forming, when 
broken, sharp edges like a flint, and its fracture has a rough earthy appearance, 
being composed of very fine grains. In most parts it is of different shades of white 
or ash colour : but in others it inclines to livid, and still more often to red, but it is 
seldom, that the redness extends over a whole rock, it is generally confined to layers 
alternating with others, that are parallel and white, or it is confined to spots or 
flakes on a white ground. Such more resemble the stones commonly called jasper; 
but whether it could be wrought, or take a polish, I cannot say, having been unable 
to procure a workman. 
This jasper, or hornstone, sometimes has larger grains, so that each is very dis- 
tinguishable to the naked eye, and then it approaches near some of the quartz, 
which becomes granular ; but there are other stones, which are a kind of intermediate 
between the two species, where a mealy or arid quartz approaches very near to our 
jasper ; and there are still others, which would seem to be composed of small por- 
tions of the two stones huddled together, and firmly united to form, what naturalists 
call an aggregate, as will be afterwards mentioned. 
The quartz, in its most perfect form, consists of 'a substance approaching to gta, 
the conchoidal appearances on which, when broken, are very minute" and are 
known to every one to differ from the former, who has taken ti.e pains to com- 
pare the appearance of a piece of broken glass with that of a flint The nuartz of 
which also there are many rocks, fa sometimes almost pellucid, like glass, sometimes 
red, or stained with red, just like the jasper, and sometimes livid • most of it has a 
fat unctuous appearance ; some of it approaching to the jasper, has dry, earthy 
looking particles ; hut, when broken, wants the large convexities, that distinguish that 
stone. Again other portions consist of small grains, united together, and some 
of these have the fat appearance, while others in the same stone are mealy and tliol 
form what the Mineralogists call an aggregate 2 . 
The quartz again is very often mixed with extraneous matter, and especially with 
what is called mica, which shines like gold or silver WliPn ti • • • ^ Tl 
quantities, thinly scattered through the body of the quartz the T “ ' V 
dered as simple ; and among the whole nuartz J ,x- , k ‘" ay be cons ‘- 
any size, could be found, in which a few specks of T<!ry fCW maSSeS ’ ° f 
when the stone consists of some particles of * mi& U not be shown; but 
ther, and closely united, these particles form what fa "an ' °‘ m ‘ Ca ’ heaped toge ' 
proceed to treat of these after, mentioning a “ “Seagate, and I shall 
that it does not cut for building. The fort of C m ,, mere . qUartz is so full of fissures, 
built of a or of che ratio Jurat, th e uljurara ^ * 8™* "Utoro 
z r;:z’ “ 
lo return to the aggregate stones, both what T i. „ 
granular jasper petrosilex, or hornstone n- r e called gi-anular quartz and 
though it is usual to confine that termto rock^ ?° nSldered ^ an aggregate ; al- 
matter has been aggregated. vi5> ln w ^ lc ^ m ore than one kind of 
V * hen tli e stone is compounded of glassv ■ 
hornstone, which, in such cases, I do not know how t^T^ ^ mealy quartZ ° f 
* The term Aggregate lias been recently rev’ h r* 6tlnSUlSh * the term wiU be 
J!,.!” a S ° mewhat restricted sense. jjJJ 6 ' . by Dr * Ho P e a »d Sir James Hall, 
tallites n'T 11 re8mClea SOUSe - They divide aUrnZu ^ Sir James Hal1 ’ 
— - — 
use of th e term, it seems to 
