RED OCHRE. 190 
ornaments. If skilfully cut in the form of small rose 
diamonds, although an opaque substance, it has some- 
what the appearance of a diamond. In the tombs of the 
Peruvian princes, with whom a considerable portion of 
their valuables was always interred, there have been 
found polished plates of marcasite, which appear to have 
served them as mirrors. 
This mineral is never worked as an ore of iron; and 
it is principally valued on account of the sulphur which 
can be obtained from it by means of heat ; and the 
green vitriol, or copperas (208), which it affords by ex- 
posure to the air. 
Ignorant persons frequently mistake iron pyrites for 
gold- but it is easily distinguished from that precious 
metal by its brittleness. It breaks when hammered, 
whereas gold is malleable, or may be extended by ham- 
mering: it also strikes fire with steel, which gold will 
not. 
237. RED OCHRE, REDDLE, or RED CHALK, is 
an iron ore of blood-red colour, ^j n 'j/ is sometimes found in 
powder, and sometimes in a hardened state. It has an earthy 
texture, and stains the fingers when handled. 
The principal use of red chalk is for drawing : the 
coarser kinds are employed by carpenters and other 
mechanics, and the finer kinds by painters. For the 
latter purpose it should be free from grit, and not too 
hard. In order to free it from imperfections, and render 
it better for use, it is sometimes pounded, washed, 
mixed with gum, and cast into moulds of convenient 
shape and size. 
Under the name of reddie, this substance is much 
used for the marking of sheep ; and (when mixed with 
oil) for the painting of pales, gates, and the wood- 
work of out-buildings. 
Another kind of iron ore, or rather a compound of 
the ores of iron and manganese, is called umber. This 
mineral, which is of a brown colour, is found in beds in 
the island of Cyprus, and is used as a kind of paint both 
in a raw state and burnt. 
