
AH ARKDNHSS—-TENACITY—SPECIFIC GRAVITY. 63 
2. PHYSICAL PROPERTIES OF 
MINERALS. 
THE physical properties referred co in the description and 
- determination of minerals are here treated under the following 
heads: (1) Hardness; (2) Tenacity; (3) Specific Gravity ; 
(4) Refraction, Polarization; (5) Diaphaneity, Color, Lustre; 
(6) Electricity and Magnetism; (7) Taste and Odor. 
1. HARDNESS. 
The comparative hardness of minerals is easily ascertained, 
and should be the first character attended to by the student in 
examining a specimen. It is only necessary to draw a file 
across the specimen, or to make trials of scratching one with 
‘another. As standards of comparison the following minerals 
have been selected, increasing gradually in hardness from talc, 
which is very soft and easily cut with a knife, to the diamond. 
This table, called the scale of hardness, is as follows : 
1, tale, common foliated variety; 2, rock salt ; 3, calcite, 
transparent variety ; 4, flworite, crystallized variety ; 5, apatite, 
transparent crystal; 6, orthoclase, cleavable variety ; 7, quariz, 
transparent variety ; 8, éopaz, transparent crystal ; 9, sapphire, 
cleavable variety; 10, deamond. | 
If, on drawing a file across a mineral, it is impressed as easily 
as fluorite, the hardness is said to be 4; if as easily as ortho- 
clase, the hardness is said to be 6; if more easily than ortho- 
clase, but with more difficulty than apatite, its hardness is de- 
scribed as 54 or 5°5, | 
The file should be run across the mineral three or four times, 
and care should be taken to make the trial on angles equally 
blunt, and on parts of the specimen not altered by exposure. 
Trials should also be made by scratching the specimeu ‘under 
examination with the minerals in the above scale, since some- 
times, owing to a loose aggregation of particles, the file wears 
down the specimen rapidly, although the particles are very 
hard. - : 
In crystals the hardness is sometimes appreciably different in 
degree in the direction of different axes. In crystals of mica 
