The
test of relative hardness is a very important one for ascertaining the
species of precious stones, on account of the facility of its
application. Its principle is the fact that the native crystal of any
species will scratch all ill the scale below itself. Thus the
Diamond, standing highest (10.) scratches all the rest. The following
is the received scale: 9.'Corundum : Sapphire, Ruby; 8. Brazilian
Topaz; 7. Bock-crystal; 6. Adularia; 5. Asparagus-stone; 4. Fluor-Spar,
&c.
The
test of the relative specific gravity of the different species, a
criterion upon which our modern mineralogists lay so much stress, and
which they claim as a discovery of their own, was well known and
resorted to by the Persian jewellers six centuries ago, and if then,
doubtless at a much earlier date.
Ben
Mansur's notice of this point is so curious as to demand its insertion
at length :—" Of the relations of certain precious stones to others. Abu Rihan pretends to have discovered by experiment that one miscal of the Blue Jacut stands in equal proportion with five dank and three tissu of the Bed Jacut ; with five dank and two and a half tissu of the Laal ; with four dank minus one tissu of Coral ;
