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116 SALTS OF LIME. 



This species takes on a great variety ot forms and colors, 

 and has received names for the more prominent varieties. 



Iceland spar. — Transparent crystalline calc spar, first 

 brought from Iceland. Shows well double refraction. 



Satin spar. — A finely fibrous variety with a satin luster 

 Receives a handsome polish. Occurs usually in veins 

 traversing rocks of different kinds. 



Chalk. — White and earthy, without luster, and so soft as 

 to leave a trace on a board. Forms mountain beds. 



Rock milk. — White and earthy like chalk, but still softer, 

 and very fragile. It is deposited from waters containing 

 lime in solution. . 



Calcareous tufa . — Formed by deposition from waters like 

 rock milk, but more cellular or porous and not so soft. 



Stalactite, Stalagmite. — The name stalactite is explained 

 on page 54. The deposits of the same origin that covei 

 the floor of a cavern, are called stalagmite. They gen 

 erally consist of different colored layers, and appear banded 

 or striped when broken. The so-called " Gibraltar rock'' 

 is stalagmite from a cavern in the rock of 'Gibraltar. 



Limestone is a general name for all the massive varieties- 

 occurring in extensive beds. 



Oolite, Pisolite. — Oolite is a compact limestone, consist- 

 ing of small round grains, looking like the spawn of a fish ; 

 the name is derived from the Greek don, an egg. Pisolite, a 

 name derived from pisum, the Latin for pea, differs from 

 oolite in consisting of larger particles. 



Argentine. — A white shining limestone consisting of 

 laminae a little waving, and containing a small proportion of 

 silica. 



Fontainbleau limestone. — This name is applied to crystals, 

 of the form in figure 4, containing a large proportion of sand, 

 and occurring in groups. They were formerly obtained at 

 Fontainbleau, France, but the locality is exhausted. 



Granular limestone.— -A limestone consisting of crystal- 

 line grains. It is called also primary limestone. The 

 coarser varieties when polished constitute the common white 

 and clouded marbles, and the material of which marble 

 buildings are made. The finer are used for statuary, and 



What is Iceland spar ? What is chalk ? How does satin spar under 

 this species differ from that which is a variety of gypsum 1 What ia 

 calcareous tufa % How are stalactites and stalagmite formed ? Wha* 

 is limestone ? What is oolite ? What is said of granular limestone ? 



