THE TROPICAL AGRICULTURIST. [Sfpt. t, 189,. 
10 
Apatite ... 
... 5 
9 
Fluorspar 
... 4 
8 
Calcite ... 
... 3 
7 
Kock Salt 
0 
6 
Talc 
The following is the Common Mineralogies] 
scale of hardness : — 
Diamond 
Sapphire 
Topaz ... 
Quartz ... .. 
Felspar ... 
Gkrygoberyl, 
The ehrysoberyl includes the eymophane or 
true cats' eye ; also known as the oriental 
chrysolite, and the alexandrite. 
The hardness of this stone is 8\">, its specific 
gravity varies from 3 - 644 to 3-8-1, and its che- 
mical composition is as follows : — 
Alumina ... ... 76 
Glucina ... ... 18 
Ferrous oxide ... 4 
Chromium oxide ... traces 
100 
Corundum. 
Corundum includes besides the common mineral 
of that name, the sapphire, ruby, oriental 
amethyst and the oiiental topaz. 
The sapphire, oriental amethyst, and oiiental 
topaz, have a hardness of about 9- The hard- 
ness of the ruby is 8 - 8. The specific gravity 
of these valuable forms of corundum is about 4. 
In chemical composition they consist almost 
entirely of oxide of aluminium with traces of 
oxide of iron and of silica. 
Quartz. 
Many precious stones consist almost entirely 
of quartz. The purest forms of quartz, such as 
rock crystal, milky quartz, cairngorm and 
amethyst vary in specific gravity to an appre- 
ciable extent, thus : — 
Milky quartz ... 2-642 
Pure rock crystal .. 2-650 
Brown cairngorm ... 2-fi56 
Amethyst ... ... 2-659 
Very dark amethyst ... 2-662 
The hardness of these forms of quartz is 7. 
Garnet. 
The Ceylon garnets are essonite or cinnamon 
stone, almandine and carbuncle. The last men- 
tioned does not indicate a distinct variety ; but 
merely the form given to the almandine when cut 
en cabochon. Pyrope is also found in Ceylon. 
The hardness of essonite is 7. Its specific 
gravity varies from 3 642 to 3 649. 
The hardness of almandine is 7*3 to 7'5, and 
the specific gravity 4-2. 
The hardness of pyrope or blood red garnet 
is 7 - 5, and the specific gravity 3 7 to 3 -8. 
Chemical Composition of Garnets. 
Pyrope or -"Magnesia Iron 
Lime Aluminium Garnet. 
Ceylon Essonite or 
Lime Aluminium 
Garnet. 
Almandine or Iron 
Aluminium Garnet. 
Silica... 
40- 
Silica ... 
. 36 
Alumina 
. 23- 
Alumina 
. 21 
Iron oxides 
. 3 7 
Iron oxides 
. 34 
Lime ... 
. 30-6 
Manganese oxides 
1 
Other substances 
2-7 
Magnesia 
. 4 
Lime ... 
2 
100-0 
98 
Silica 
Alumina 
Iron protoxide... 
Manganese protoxide 
Chromium ttesquiosulf 
Magnesia 
Lime 
I ;.. linn ifl 
Santa Ft?. 
41 '4 
42 1 
22 3 
19 4 
9 9 
14-9 
2 6 
•4 
4 5 
2ti 
150 
14-0 
5 3 
5- 
101, -o 
98-4 
Uwtrowitc <>r Lime-Chioiniiim 
Silica.. 
Alumina 
Chromium oxide 
Lime... 
Garnet. 
37 
6 
23 
33 
99 
Beryl. 
Iteryl includes the aquamarine and emerald of 
which the former is found in Ceylon. 
The baldness of beryl is from 7'5 to 8, and 
the specific gravity 27- The following is the 
approximate composition of beryl : but in addi- 
tion to the constituents given, oxide of iron, 
water ami traces of other compounds as oxide 
of chromium, to the last of which the color of 
the emerald is considered to Ik* due, arc present: — 
Analysis of Berj L 
per cent. 
Silica ... ... 66-8 
Alumina ... 191 
Glucina ... 14 1 
100 0 
Spinel, 
Spinels are of various colors : the red is called 
the spinel ruby, or lialas ruby, the orange and 
flame colored are called rubicelle spinels, the 
violet and purple are called almandine spinels, 
and the black spinel of Ceylon is called pieo- 
naste. The hardness of the spinel is 8 and its 
specific gravity from 3-590 to 3 - 715. It con- 
sists of : — 
Alumina ... 72 
Magnesia ... 28 
100 
In black spinel the magnesia is to a great 
extent replaced by ferrous oxide, of which as 
much as 20 per cent has been found. 
lolite. 
Iolite, also called dichroite and saphir d' ean, 
is a Ceylon stone remarkable for its beautiful 
changes of color when viewed from different 
directions. Blue, gray and straw colored tints 
are thus exhibited by the same crystal. The 
hardness of this stone is above 7 and it. specific 
gravity from 2 6 to 2 66. 
Its average composition is : — 
Silica ... ... 49 
Alumina .. ... 32 
Ferrous oxide ... 7 
Magnesia ... 9 
Tourmaline. 
Indicolite or the blue tourmaline does not 
appear to be found in Ceylon ; but the colorless 
variety achroite, the black or schorl, and the 
red or rubellite, are all found in the island. 
The hardness of tourmaline is 7 "5, its specific 
gravity varies from 3 to 3'25. The composition 
is very complicated, as Bammelsberg's analysis 
of a Brazilian specimen will show. 
