252 Reétxamination of American Minerals. 
from the side. It sometimes happens that these slender crys- 
tals are crossed by one of the same diameter, and less length, 
firmly attached in the manner of a cross. 
But of all remarkable crystallizations is one, where the small 
prisms are so arranged as to form a perfect double spiral arranged 
around an axis, (fig. 3); the specimen is three inches in length 
2. 
and ths of an inch in diameter, with the space of a 4th of an 
inch between each turn of the spiral. The spiral arises from one 
crystals are sometimes curved in a very remarkable manner. 
Another thing to be remarked in connection with the calcite of 
this mine, is its singular associations; thus, we find groups of 
hexagonal prisms where a small cubical crystal of fluor, about the 
z'sth of an inch, is inserted ina small pit in the summit of almost 
every crystal (fig. 4) without the occurrence of fluor spar on 
any other parts of the crystal. These crystals + 
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The summit never closes entirely at the centre , 
the fluor spar remaining visible on one side, Ue al 
and where there is no crystal of fluor spar the | 
extremity of the dog-tooth spar is frequently seen. 
Other groups of calcite crystals, have minute crystals of iron 
pyrites in the three faces of the summit, arranged near and per- 
a, 6 
fectly parallel to the alternate edges as seen in figure 5. Every 
oe in the group is thus furnished with a set of crystals | 
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