36 
NORTH GALLERY. 
[upper 
Cases 5 to 12 contain such of these compounds as consist of com- 
binations of metals with elements of the Sulphur class, i. e. with Sulphur- 
Selenium, Tellurium, Arsenic, and Antimony. Of these compounds 
there are several groups, varying in complexity of composition, from 
the simple Sulphides (or compounds of Sulphur with a metal), such as 
Galena, the most important ore of Lead ; Cinnabar, the ore of Mer- 
cury ; and the Sulphides of Silver, of Copper, of Zinc, Iron, Antimony, 
&c. ; or the Arsenides, e. g. Smaltine (Arsenide of Cobalt), &c. ; up to the 
complicated groups of elements which combine to form such minerals 
as Fahl-ore (or Grey Copper), the ''Red Silver ores," '' Bournonite," &c. 
In these Cases will be observed, by the side of the important ores 
alluded to, many minerals interesting for their rarity, or remarkable 
for the size and form of the individual specimens. To the former 
class belong among others the Selenides, compounds of Selenium with 
L,ea([ (Clausthalite), with Mercury (Onofrite), &c. ; and Greenockite, 
the sulphide of the metal Cadmium, a beautiful yellow mineral of 
great lustre, the produce of Scotland; while to the latter belong 
specimens under ^tlmost every important species. 
The rest of the collection, to Case 58,-. consists of minerals containing 
Oxygen as one of their chemical constituents, a class necessarily very 
large on a planet with an atmosphere consisting in considerable propor- 
tion of so chemically energetic a gas as Oxygen. 
Tables 13 to 24 inclusive, contain the Oxides, properly so called, 
tiiat is to say, metals and other elements in direct combination with 
Oxygen, in which no more complex constitution is discernible. This 
extensive class includes some very important minerals. Such is Ciqjvite, 
ihe "red oxide" (sw5oxide) of copper; while specimens of Tenorite 
illustrate the mineral form of the jJ^otoxide of that metal. The iron ore 
of Elba, belonging to the species properly called Hcematite, is conspicu- 
ous for its beautiful iridescent tarnish and crystalline forms, while the 
hydrated varieties of this oxide (the sesquioxide) of Iron, are illustrated 
by LimnitG (brown Haematite) and Gothite. The series of minerals 
allied in chemical constitution and crystalline form to the rich ore which 
furnishes the loadstone-^the magnetic oxide of Iron — includes Chromite 
and Franklinite. It also includes the Spinels. Among these are 
specimens of the dark red or spinel Ruby, the rose-tinted balasRuby, the 
orange-red ruhicelle, and the hlack pleonaste ; some in crystals and some 
cut as gems, which are only inferior in beauty to the true Oriental Ruby. 
Of the latter mineral — the " Oriental " Ruby — specimens in the crystal- 
line, as well as in the cut form, are included under the species Corundum. 
This species, which consists of more or less pure Alumina (sesquioxide 
of Aluminium), comprehends the most resplendent and varied series of 
gems in the whole mineral kingdom. The range of its extensive 
colour-suite is shown in the (blue) Sapphire, the (red) Ruby, the (green) 
" Oriental " Emerald, Oriental Amethyst, &c., &c. The Chrysoberyll, 
called also Cymophane, from the occasional appearance of a cloudiness 
in some directions of its crystalline form, finds its place here. It is a 
mineral scarcely inferior in hardness and in lustre to the Sapphire itself, 
and interesting from its crystallising in forms incompatible with those 
