24 
MR. J. T. HOTBLACK ON PRECIOUS STONES. 
protoxide of iron 6.25. The colours are brown, green, yellow, 
sometimes blue and black. It is sold as chrysolite or hyacinth, 
according to colour. It is too soft to be of any value, but is cut 
into jewels and ornaments principally at Naples and Turin. 
Felspar, or Feldspar. 
This substance is never sold in jewellery under this name, it is 
found in tabular crystals and in cleavable masses, the best is no 
more than 6 in the scale of hardness, and the S.G. is 2.4 to 2.6. 
Its composition is about: Silica 64.0, alumina 19.5, potash 15.0. 
When pearly white and chatoyant it is the moon stone, when 
opalescent it is called Ceylon opal or water opal, when pale yellow 
with minute golden spangles it is sun stone, when opaque green 
(from trace of copper in composition) it is the Amazon stone. At 
one time the moon stone was fashionable in this country, but is 
now seldom seen. The moon stone was also much esteemed by the 
ancients. 
Labradorite, or Labrador Felspar 
has a hardness of 6, S.G. 2.65 to 2.75, and its composition is 
about: Silica 55.0, alumina 27.0, lime 11.0, soda 5.0. When 
vitreous and pearly, greenish to white, is chatoyant ; it is called 
by jewellers by its true name labradorite. It is found in Scotland 
and Ireland, as well as in many foreign countries. Though not much 
used in jewellery, it is manufactured into brooches, bracelets, &c., 
but a great deal of skill is necessary to divide the stone so that the 
iridescence, on which its beauty depends, is displayed to the best 
advantage. 
Lapis Lazuli 
is found sometimes in small crystal, but generally massive, and is 
I think, the softest of the crystals used in jewellery, being only 
5.0 in hardness, and about 2.35 to 2.45 in S.G. Its composition 
is variable. I find : 
Silica ... 
Alumina 
Lime ... 
Carbonic Acid 
Sulphuric Acid 
Protoxide of Iron 
Soda ... 
46.0 45.5 
14.5 37.5 
17.5 3.5 
10.0 
4.0 3.5 
3.0 
9.0 
