70 
THE PRINCIPAL FLOOR. 
Zinc Ores. 
Cases 11 and 12. — The most widely-diffused ore of this metal 
is the sulphide called Zinc blende , from the German blenden, to 
dazzle, in allusion to the high lustre which this mineral often 
presents. Blende is generally associated with the ores of lead, 
and frequently with those of copper and tin. In a state of purity 
it is transparent and almost colourless, as seen in some of the 
specimens in this case ; but generally the blende of this country 
is mixed with a variable amount of sulphide of iron, which imparts 
to it a dark colour, whence it is called by the English miners 
Black Jack . In some districts the presence of zinc is deemed 
by the miners unfavourable, and they speak of “Black Jack 
cutting out the lode/' In others it is thought to be a favourable 
indication, and we often hear that “ Black Jack rides a good 
horse.” 
More valuable as an ore, but much less abundant than the 
sulphide, is tbe carbonate of zinc usually known as Calamine. 
This mineral rarely occurs crystallized, but is usually found in 
deposits of mammillated, botryoidal, and stalactitic forms, of 
which some fine examples are exhibited from Alston Moor. 
The hydrous silicate of zinc, known as Smithsonite or electric 
calamine, commonly occurs associated with the carbonate, with 
which it is not unfrequently confounded. Attention may be 
directed to a fine specimen of a blue cupreous variety of this 
species from Cumberland. 
Cadmium. 
Case 12. — With the ores of zinc will be found some specimens 
of the rare Scotch mineral called Greenockite , which is a sulphide 
of cadmium occurring in yellow lustrous crystals of hexagonal 
form. The usual sources of cadmium and its applications have 
been noticed at p. 57. 
Manganese. 
Case 13. — Although not occurring in this country in regular 
deposits or in very considerable quantity, the ores of manganese 
have, however, been worked in several localities near Tavistock, 
and at Launceston, at several mines not far from Exeter, in the 
Mendip Hills, and in Warwickshire. 
Manganese is employed in glass manufacture as a decolouring 
agent, in the manufacture of pottery as a pigment, and it is 
likewise used in the manufacture of Spiegeleisen and ferro- 
manganese. In the preparation of chloride of lime and in 
bleaching, manganese is very largely used, being employed for 
the purpose of liberating the chlorine from the hydrochloric 
acid or the salt (chloride of sodium) with which it is mixed for 
this purpose. 
Pyrolusite, or binoxide of manganese, has received its name 
from the Greek (pur, fire and luo, to wash ) in allusion to its 
