There
is also much confusion as to the difference between sard and sardonyx,
although the name is suggestive. The sard is a solid color stone
similar to the carnelian, only of a darker, brownish-red color; the
sardonyx is the same stone with underlying strata of a lighter or other
colors, similar to the onyx.
As
many of the features by which a mineral is recognized in the natural
state are obliterated in the cutting, and the tests for hardness and
specific gravity are not always possible to the dealer, he must rely
very largely on the instinctive judgment which comes of familiarity,
and a few simple facts which serve to guide him. A chapter has been
devoted to the differences existing between stones similar in color and
general appearance when cut, and tables appended, showing the various
methods by which their identity may be established.
