Gemstone Terminology Test #1

Front 1

Gem/Gemstone

Back 1

see pg. 10 of book

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Gemology

Back 2

Internationally, the science of gemstones is most commonly referred to as gemology

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Colored Stone

Back 3

Colored stone is a trade term for all gemstones except diamonds (even those that are colorless).

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Rock

Back 4

With regard to gems, a rock is a natural aggregate of two or more minerals. Lapis lazuli is an example of a gem that is classified as a rock. It forms independent geological bodies of greater expansion and comprises both solid rock and accumulated unconsolidated rock.

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Semi-Precious Stone

Back 5

The term semi-precious has generally fallen out of use because of its derogatory meaning. Formerly, one meant with this term the less valuable and not very hard gemstones, which one opposed to the "precious" stones. "Precious" and "semi-precious" are adjectives, however, that cannot be adequately defined to distinguish between gems.

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Imitation

Back 6

Imitations are made to resemble natural or synthetic gem materials, completely or partially manmade. THey imitate the look, color, and effect of the original substance, but they possess neither their chemical nor their physical characteristics. To these belong - strictly speaking - also those synthetic stones that do not have a counterpart in nature (for instance, fabulite or YAG). However, in the trade these are oftencounted as synthetic stones.

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Jewel

Back 7

Every individual ornamental piece is a jewel. Generally, a jewel refers to a piece of jewelry containing one or more gems set in precious metal. Sometimes, it can also refer to cut, unset gemstones.

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Crystal

Back 8

A crystal is a uniform body with an ordered structure, i.e., a strict order of the smallest components (the atoms, ions, or molecules) in a geometric crystal lattice. The varying structures of the lattice together with the chemical components, are the causes of the varying physical properties of the crystals and therefore also of the gems.

Front 9

Crystallography

Back 9

Crystallography is the science of crystals

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Mineral

Back 10

A mineral is a naturally occurring, inorganic, solid constituent of the earth's (or other celestial body's) crust. Most minerals have definite chemical compositions and crystal structures.

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Mineralogy

Back 11

Mineralogy is the science of minerals

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Petrography

Back 12

Petrography is the descriptive science of rocks, typically utilizing a petrographic microscope or other instruments. The term petrography is often used more comprehensively to mean the same as petrology.

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Petrology

Back 13

Petrology is the science of the origin, history, occurrence, structure, chemical composition, and classification of rocks. SOmetimespetrology is loosely used to mean the same as petrography.

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Species

Back 14

A mineral species is distinguished by a specific combination of chemical composition and crystal structure (e.g., diamond is carbon in a cubic structure). This combination produces the mineral's distinctive optical, physical, and chemical properties.

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Stone

Back 15

Popularly, stone is the collective name for all solid constituents of the earth's crust except for ice and coal. For jewelers and gem collectors, the word stone means only gemstones. For the architect, on the other hand, it means the material used for constructing buildings and streets. In the science of the earth, geology, one does not talk of stones, but of rocks and minerals.

Front 16

Synthesis

Back 16

Short term for a synthetic stone.

Front 17

Synthetic Stone

Back 17

Synthetic gemstones (in short called syntheses) are crystallized manmade products whose physical and chemical properties for the most part correspond to those of their natural gemstone counterparts. This term is also used by the gemstone trade for those synthetic stones which do not have a counterpart in nature (for instance, fabulite or YAG). In fact, these stones are properly termed imitations.

Front 18

Variety

Back 18

By a variety, one understands in the case of gemstones a modification which distinguishes itself through its look, color, or other characteristics from the actual gemstone species.

Front 19

Carat

Back 19

The weight used in the gem trade since antiquity

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Gram

Back 20

The weight measure used in the trade for less precious gemstones and especially for rough stones

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Grain

Back 21

Formerly, the weight measure for pearls. It corresponds to 0.05g or 1/4ct. Today, it is increasingly substituted by use of the carat.

Front 22

Momme

Back 22

The old Japanese measure of momme (=3.75g=18.75ct) for cultured pearls is hardly sued anymore except by wholesale distributors.

Front 23

Luster

Back 23

The luster of a gem is caused by external reflection. It is dependent on the refractive index of the stone and the nature of the surface. Generally, the higher the refraction, the higher the luster. Gems without luster are described as dull. However, there is no unified opinion regarding the influence of color on the luster.

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Metallic luster

Back 24

the strongest luster of all. Just like polished metal or the luster of aluminum foil. Only existent with opaque gemstones, particularly with pure metal, sulfides, and some oxides. Meets a refractive index of about 2.6 to more than 3.

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Diamond Luster

Back 25

Sparkling luster as with cut diamonds or with lead crystal glass. Only existent with transparent or translucent gemstones. Meets a refractive index of about 1.9 to 2.6.

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Greasy Luster

Back 26

Like the shine of grease spots on paper. Holds true for turbid stones with a low refractive index. Not widely common with gemstones, except on cleavage planes.

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Pearly Luster

Back 27

Like the shine of mother-of-pearl, the innermost iridescent layer of some mussel, oyster, and snail shells. Especially found on cleavage planes of gemstones with perfect cleavage.

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Silky Luster

Back 28

Intense ray of light, as can be observed with natural silk. Appears with parallel fibrous gemstones or corresponding aggregates.

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Waxy Luster

Back 29

Dull shine of gemstones with coarser unevenness, such as flint.

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Resinous Luster

Back 30

Resin-like, less intensive luster as with amber. Rare with gemstones.

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Vitreous Luster

Back 31

Just like the shine of simple window glass. Meets a refractive index of about 1.3. With glass imitations, depending on the type of glass used, the refractive index reaches up to 1.9, that is, it almost reaches diamond luster.