in the smaller sizes.
In this case the back must be tested.

One should never pass a file rudely across the corners or edges of the
facets on any stone that may be genuine, as such treatment really
amounts to a series of light hammer blows, and the brittleness of most
gem stones would cause them to yield, irrespective of their hardness. It
should be remembered that some genuine stones are softer than a file, so
that it will not do to reject as worthless any material that is attacked
by a file. Lapis lazuli (5), sphene (5), opal (6), moonstone (6),
amazonite (6), turquoise (6), peridot (6-1/2), demantoid garnet (6-1/2)
(the "olivine" of the trade), and jade (nephrite) (6-1/2), are all more
or less attacked by a file.

TABLE OF HARDNESS OF THE PRINCIPAL GEM-STONES

10. Diamond.
9-1/2. (Carborundum.)
9. Sapphire and ruby (also all the color varieties of
sapphire).
8-1/2. Chrysoberyl (alexandrite).
8. True topaz and spinel (rubicelle, balas ruby).
7-1/2. Emerald, aquamarine, beryl, Morganite, zircon (jacinth and
true hyacinth and jargoon), almandine garnet.
7-1/4. Pyrope garnet (Arizona ruby, cape ruby), hessonite garnet
(cinnamon stone), tourmaline (various colors vary from 7
to 7-1/2), kunzite (7+).
7. Amethyst, various quartz gems, quartz "topaz," jade
(jadeite).
6-1/2. Peridot (chrysolite), demantoid garnet ("olivine"), jade
(nephrite).
6. Opal, moonstone, turquoise.
5. Lapis lazuli.

LESSON IX

HARDNESS--_Continued_

MINERALS USED IN TESTING HARDNESS. For testing stones that are harder
than a file the student should provide himself with the following set of
materials:

1. A small crystal of carborundum. (Most hardware stores have specimen
crystals as attractive advertisements of carborundum as an abrasive
material, or the Carborundum Co., Niagara Falls, N. Y., will supply
one.)

2. A small crystal of sapphire (not of gem quality, but it should be
transparent and compact. A pale or colorless Montana sapphire can be had
for a few cents of any mineral dealer).

3. A small _true topaz_ crystal. (The pure white topaz of Thomas
Mountain, Utah, is excellent; or white topaz from Brazil or Japan or
Mexico or Colorado will do. Any mineral house can furnish small crystals
for a few cents when not of specially fi