I 



THE PROPERTIES OF MINERALS. 679 



Examples of fracture. 



Conchoidal. — Xovaculite, Magnet Cove, Arkausas. (Cat. Xo. 46280, U.S.N.M.) 

 £ren. — Chlorite, London County, Virginia. (Cat. No. 12352, U.S.N.M.) 

 Unereii. — Lepidolite, Aubuin, Maine. (Cat. No. 16157, U.S.N.M.) 

 Hackly. — Hematite, Dun Mountain, New Zealand. (Cat. No. 17792, U.S.N.M.) 



HARDNESS. 



This is the degree of resistauce a miueral ofters to abrasion. It is 

 usuallj' referred to an arbitrary scale of ten minerals showing- a regular 

 gradation iu hardness from l,talc, the softest; 12, gypsum; 3, caleite; 4, 

 fluorite; 5, apatite; 6, orthoclase; 7, quartz; 8, topaz; 1), corundum, 

 to 10, diamond, the hardest. 



TENACITY. 



The degrees of tenacity may be classed as brittle, sectile, malleable, 

 flexible, and elastic. 

 Examples of these are found in the following specimens: 



Caleite, Oxbow, Nevr York (Cat. No. 16883, U.S.N.M.), brittle; the mineral sepa- 

 rates in grains or a powder ou attempting to cut it with a knife. 



Seleuite, Truckee Mountains, Nevada (Cat. No. 18374, U.S.N.M.), sectile; the 

 mineral may be cut without falling to pieces, but pulverizes under the hammer. 



Copper, Copper Falls, Michigan (Cat. No. 12061, U.S.N.M.), malleable; slices may 

 be cut oil' and llattened out under the hammer. 



Talc, Chester County, Pennsylvania (Cat. No. 12002, U.S.N.M.), flexible; the min- 

 eral will bend, but remains bent after the bending force is removed. 



Muscovite, Peunsbury, Pennsylvania (Cat. No. 83483, U.S.N.M.), elastic; the min- 

 eral after bending will spring b.ack to its original position. 



C — CHARACTERS DEPENDING UPON MASS OR VOLUME. 



SPECIFIC GRAVITY. 



This is the density of the mineral compared with that of distilled 

 water at 4° C. The wide range in the specific gravity of minerals is 

 sho\^n by a series of specimens, and their relative densities shown by 

 cubes, taking a definite volume of water as unity. 



D — PROPERTIES RELATIN(r TO HEAT, MAGNETISM, AND ELECTRICITY. 



HEAT. 



Under this head is included the expansion of minerals, their power 

 of conducting, transmitting, or absorbing lieat, and tlieir fusibilit}'. Of 

 these ijroperties fusibility is the most important, and the only one that 

 can be readily illustrated. This propeity in mineralogy is a relative 

 value, determined b}- comparison with a fixed scale, showing a regular 

 gradation from 1, stibnite, the most readily fused; 2, natrolite; 3, gar- 

 net; 4, actinolite; 5, orthoclase, to 6, bronzite, the most difficult. 



MAGNETISM. 



All minerals are either magnetic or nonmagnetic. Magnetic min- 

 erals may be either paramagnetic, that is, attracted by the poles of a 



