

METALLIC ORES. 203 



of the shops is obtained from naHve bismuth. Native silver 

 native mercury, and native copper, are sometimes abundant, 

 but are far from being the main sources of these metals. 

 The other native metals are mineralogical rarities. Perhaps 

 we should except from this remark native iron, which con- 

 stitutes large meteoric masses, though very rarely if ever 

 seen of terrestrial origin. 



Their associations and impurities. — The ores of the 

 metals are often much disguised by mixtures with one an- 

 other or with earthy material. Thus a large part of the 

 iron ore worked in England and this country is so mixed 

 with clay or silica, that its real character might not be sus- 

 pected without some experience in ores. 



Occasionally ores contain phosphate of iron or some arsen- 

 ical ores or certain sulphurets, scattered through them ; and 

 on account of the difficulty of separating the phosphorus, sul- 

 phur, or arsenic, the ore is renderec comparatively useless. 

 By this intimate mixture of species, the difficulties of reducing 

 ores are much increased. 



When different ores are not intimately commingled, they 

 are frequently closely disseminated together through the 

 rock. We find ores of lead and zinc often thus associated ; 

 also of cobalt and nickel ; of iron and manganese ; the ores 

 of silver, lead and copper, and often cobalt and antimony ; 

 platinum, iridium, palladium and rhodium. 



Position in rocks. — Metals and their ores occur in the 

 rocks in different ways : 



1. In beds or layers between layers of rock, as some iron 

 ores ; 



2. Disseminated through rocks in grains, nests, or crystals, 

 or extended masses, as is the case with iron pyrites, cinna- 

 bar, or mercury ore, and much argillaceous iron ; 



3. In veins, intersecting different rocks, as ores of tin, 

 lead, copper, and nearly all metallic ores ; 



4. Very frequently, metallic ores, instead of occurring in 

 true veins, are found in rocks near their intersection with a 

 mass or dike of igneous rock, as in the vicinity of a por- 

 phyry or trap dike. This is the case with much of the cop- 

 per ore in Connecticut and Michigan, as well as with much 



What is said of native iron ] How are ores often disguised ? Explain 

 lijr example. How do they occur together ? What is an effect of this 

 mixture 1 What are the positions of ores in the rocks ? 



