426 | oo Diamonas. [July, 
into competition. In 1660, during the reign of Louis XIII, Car- 
dinal Mazarin had the first diamonds cut for the French crown. 
Within late years the machinery for cutting diamonds has been 
greatly improved, so that the Ko-hi-noor was re-cut in the space 
of thirty-eight days, while the cutting of the Regent had 
required two years. 
Two styles of cutting are employed in shaping the diamond, 
the rosette and the éri/éant. The foundation for the former is the 
number two multiplied by three, for the latter the number four. 
A complete rosette cut will cover the entire diamond with faces 
of equal, triangular shape, whiie the brilliant presents a flat sur- 
face, surrounded by facets and a deep pyramidal or conical 
body. Numerous combinations of faces are added to increase 
the action of refraction. As will readily be seen from the most usual 
forms of crystallization of smaller diamonds, the brilliant cut can 
be executed with the least loss of material. It certainly presents 
the stone to best advantage. 
Turning aside from the historical associations of the diamond, 
we have yet to consider its chemical and physical properties. 
Among all minerals the diamond is by far the hardest. Next 
to it are the various corundum species, ruby, sapphire and others. 
This alone, to a mineralogist, is sufficient to distinguish it. Its 
specific gravity is 3.5295, about the same as topaz. The index of 
refraction is 2.439. Expressing the power of refraction in a 
more tangible manner, we may say that if we have a glass lens 
of certain dimensions which magnifies five diameters, an equal 
lens of diamond would magnify eight diameters. Upon being 
rubbed the diamond exhibits vitreous electricity. By passing an 
electric spark over a diamond, the stone may be rendered phos- 
phorescent, and retains this quality fora short time. This fact, prob- 
ably, has given rise to the popular supposition that all diamonds 
must “shine” in the dark. When looking at a cut diamond it is 
a good plan to have a dark back-ground, as the brilliancy of the 
flash thereby becomes more prominent. 
Diamond crystallizes in the isometric system, and shows 
“numerous combinations. Most frequently occurring is the 
octahedron with many combinations. Dodecahedra are found 
simple and in combination. Perhaps no other mineral exhibits 
_ so many different forms belonging to the isometric system as this. 
ne. Twins and hemihedral crystals are frequently found. Char- 
