78 GEMS OF AUSTEALIA. 



hammer on an anvil','''' and they try the experiment accordingly ; 

 when the diamond, of course, is pounded into dust ! 



Mohs' Scale of Hardness. — 1. Talc. 2. Grypsum or rock-salt. 

 3. Calc-spar. 4. Muor-spar. 5. Apatite, or asparagus stone. 

 6. Pelspar. 7. Quartz, transparent. 8. Topaz. 9. Sapphire. 

 10. Diamond. 



Any elementary book on mineralogy will explain the method 

 of using this scale. It is sufficient now to state that to the eye 

 of a superficial observer, knowing nothing of the crystallographic 

 forms of the respective minerals, a crystal of quartz, a white 

 topaz, a white sapphire, and a diamond, have a tolerably close 

 resemblance, as respects lustre and colour, and general appearance ; 

 but by applyiag the sharp angle of one stone to the face of any 

 other, and endeavouring to scratch it, he will make no impres- 

 sion on the latter, if it be the harder of the two ; yet, if of a lower 

 scale of hardness, it will receive an indelible scratch. If two 

 specimens are the same mineral, or of the same hardness, they 

 are both slightly scratched or abraded. 



5. Another valuable test for minerals, especially gems, is the 

 ascertaining their relative weight to distilled water, which is called 

 taking their " Specific gravity." Thus, a diamond is about 3-| times 

 as heavy as water ; a sapphire, about 4 times ; a topaz, about 

 3i times ; and quartz, about 2-|- times : being severally marked 

 S.&. (specific gravity) =3-52 ; 3-909— 4-16; 3-4— 3-65 ; 2-5— 2-66. 



A remarkable proof of the accuracy, of this valuable test of 

 " specific gravity" was recently afforded the author ; who had to 

 determriie, whether a fine water- worn gem-stone of large dimen- 

 sions (exceeding the size of a pigeon's egg), found in Bass's Straits, 

 was a pale-green topaz, or an aquamarine (beryl). As no 

 experiment involving the slightest injury to the stone was 

 permitted, that of ascertaining its specific gravity was at 

 once the most satisfactory and harmless. Its weight in air was 

 317'S3 grains ; in water, 201'26 ; and, by working out the sum, 

 the specific gravity was found to be 2 '726. A cut and polished 

 aquamarine from Europe was then weighed, for the sake of com- 

 parison. Its weight in an- was 42'64 grains ; in water, 27'0 

 grains ; and by dividing the weight out of water (i.e., in air) by 

 the diff'erence of weights obtained out of, and in water (which is 

 the method of working the " specific gravity" sum) the specific 

 gravity of the latter gem was also found to be — as any person 

 can ascertain for himself — exactly the same, viz., 2'726 ; being 

 within 6-lOOOths of the weight assigned by Haidinger, the mine- 

 ralogist, to the aquamarine (beryl) : whereas the specific gravity 

 of the topaz is nearly one-fourth greater. After such a wonderful 

 coincidence in weights, could the greatest sceptic doubt that the 

 larger stone was also an aquamarine, or question the accuracy of 

 the test ? 



