K.E.Kluge published a classification of gemstones in his 1860 book Handbuch der Edelsteinkunde
, reprinted in English by Bauer in his 1904 book on Precious Stones. It's interesting to see how much opinions on value and rarity have changed over time.
True Precious Stones or Jewels
Distinguishing characters are:
great hardness, fine colour, perfect transparency, combined with strong lustre (fire), susceptibility of a fine polish, and rarity of occurrence in specimens suitable for cutting.
A. Gems of the First Rank.
Hardness, between 8 and 10. Consisting of pure carbon, or pure alumina, or with alumina predominating. Fine specimens of very rare occurrence and of the highest value.
B. Gems of the Second Rank.
Hardness, between 7 and 8 (except precious opal). Specific gravity usually over 3. Silica a prominent constituent. In specimens of large size and of fairly frequent occurrence. Value generally less than stones of group A, but perfect specimens are more highly prized than poorer specimens of group A.
10. Precious Opal
C. Gems of the Third Rank.
These are intermediate in character, between the true gems and the semi-precious stones. Hardness, between 6 and 7. Specific gravity usually greater than 2.5. With the exception of turquoise, silica is a prominent constituent of all these stones. Value usually not very great; only fine specimens of a few members of the group (cordierite, chrysolite, turquoise) have any considerable value. Specimens worth cutting of comparatively rare occurrence, others fairly frequent.
These have some or all of the distinguishing characters of precious stones, but to a less marked degree.
D. Gems of the Fourth Rank.
Hardness 4 - 7. Specific gravity 2 - 3 (with the exception of amber). Colour and lustre are frequently prominent features. Not as a rule perfectly transparent; often translucent, or translucent at the edges only. Wide distribution. Value as a rule small.
A. Crystallised quartz
a. Rock crystal
c. Common quartz
c) Cat's eye
d) Rose quartz
a. Fire opal
b. Semi opal
e. Jasper opal
f. Common opal
E. Gems of the Fifth Rank.
Hardness and specific gravity very variable. Colour almost always dull. Never transparent. Low degree of lustre. Value very insignificant, and usually dependent upon the work bestowed on them. These stones, as well as many of the last group, are not faceted, but worked by the ordinary lapidary in the large-stone-cutting works.
40. Satin spar
42. Satin-spar (gypsum
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