86 
MINERAL GALLERY. 
Native 
Elements. 
Sulphides. 
tinguished by the letters a to A. For the use of the student 
there is published an Index to the names of all the numerous 
mineral species and varieties represented in the collection, 
with references to the table-cases in which the specimens are 
placed.* 
The system of classification, which includes not only ores, 
but all known minerals, is not easy for a general visitor to 
follow, and it is thus convenient to indicate here the positions 
in the gallery of those minerals — as, for instance, precious and 
ornamental stones, and metallic ores — which have an interest 
for all; for details, reference must be made to the Mineral 
Guide. Most of these minerals occur in crystals, the forms of 
which were at one time supposed to be modifications of six 
chief types. 
I. In cases 1 and 2 are the pure metals, as Copper, Silver, 
Gold, and Platinum; and non-metals, as Sulphur, Graphite, 
and Diamond. The large symmetrical South African " Colenso " 
Diamond (fig. 58), weighing 130 carats, presented by the late 
Professor Kuskin, is worthy of special attention (case Ig). 
II. The next six cases contain minerals which have mostly a 
metallic lustre and consist of metals in chemical combination 
with elements of the sulphur or arsenic groups. 
Argentite (3d) is an important silver-ore, containing 87 per 
cent, of silver and 13 of sulphur. 
Blende (4b) is a valuable zinc-ore, and contains 67 per cent, 
of zinc and 33 per cent, of sulphur.. 
Fig. 58. — The Colenso Diamond, from South Africa. 
Preseuted by Professor John Kuskin. (Natural size.) 
* " The Student's Index to the Collection of Minerals." Price twopence. 
