GI-2: General Observation Flashcards
Transparent
Description of a material that’s capable of transmitting light so objects viewed through it appear clear and sharp.
Translucent
Description of a material that’s capable of partially transmitting light so an image seen through it appears obscure, with a vague outline.
Opaque
Description of a material that’s unable to transmit light, so an image can’t be seen through it.
Example: Turquoise
Luster
The appearance of a material’s surface in reflected light.
Depends on material’s RI, hardness, quality of polish.
What is the most common luster for transparent stones?
Vitreous
Cleavage
A smooth, flat break in a gemstone parallel to places of atomic weakness
Example: Calcite with 3 directions of cleavage
Parting
A flat break in a gemstone parallel to a twinning plane
Fracture
Any break in a gem other than cleavage or parting
Conchoidal fracture
A curved and ridged fracture in a gemstone, extending from the surface inward.
Examples: Glass
Splintery Fracture
A gemstone fracture looks lke broken wood, resulting from the fibrous structure of certain gems
Examples: Hematite and tiger’s eye quartz
Fire
The flashes of spectral color you see in a polished gem, especially a diamond
Is much easier to assess in colorless gems than in those with strong bodycolor
Dispersion
The separation of white light into spectral colors.
Is measured with RI.
Is a property that remains constant no matter how a gem material is fashioned.
What are the 3 types of surface breaks in a stone?
- Cleavage
- Parting
- Fracture
Heft
How heavy an object feels in relation to its size.
Gives an indication of physical density or specific gravity
Grades: High, Moderate, Low
What are the 2 primary ways to detect assembled stones?
- Magnification
and
- Reflected light (red ring test)
Where is best place on stone to judge transparency?
Where the stone transmits the most light
Where is the best place to judge luster?
On the surface area that has the best polish.
When a material only partially transmits light so that an image seen through it has just a vague outline, it is described as
Translucent
What is Asterism caused by?
Reflections from precisely oriented, needle-like inclusions
You should start the gem identification process with
General Observation
The cat’s-eye effect is also called
Chatoyancy
If you see a red ring during your examination of a gem it is an
Garnet-and-Glass doublet
If you have a gem where a design is engraved into the surface, record its cutting style as
Intaglio
If you observe extreme fire in a colorless gem, it might be
Synthetic Rutile
Heft cannot be tested on a gem if it is
Mounted
The degree to which a material transmits light is its
Transparency
