Diamonds & Diamond Grading
questions and answers
Aggregate✔✔A solid mass of individual, randomly oriented crystals, intergrown, or
held together by a natural binding agent.
Fair✔✔Total depth percentage between 51% to 70.9%
Naif✔✔The natural unpolished surface of a rough diamond
Point Naif✔✔A seventeenth-century term for a diamond octahedron or other crystal
shape on which the natural faces are apparent. (Assignment 9)
Bast✔✔Frosted rough diamond. "Bark" in Dutch. (Assignment 9)
Cross Working✔✔Placing the bezel and pavilion facets on round and fancy shapes.
Sometimes combined with blocking, especially on smaller stones. Also called cross
cutting. (Assignment 9)
Foss✔✔Irregular furrow or groove in the surface of a diamond, characteristic of
diamond crystals in the gray color range. (Assignment 9)
Sharp✔✔A small diamond with a sharp edge, cemented into a dop and used to kerf
another diamond in preparation for cleaving.
Or, a small diamond used to brute diamonds or round up a girdle in the final stages
of polishing.
Three point diamond✔✔A diamond with its table nearly parallel to a possible
octahedral face. (Assignment 9)
Twisted Stone✔✔A diamond with grain layers that are not on parallel planes, or one
with partial twinning. (Assignment 9)
Twisting✔✔A blocking technique in which the diamond is turned to position the
softest polishing direction against the polishing wheel. (Assignment 9)
Two point diamond✔✔A diamond on which the table has been polished parallel to a
dodecahedral plane. (Assignment 9)
Water✔✔A historic term once used in Europe to describe either the color or the
transparency of a diamond
Four point diamond✔✔A diamond with the table parallel to a possible cubic face.
(Assignment 9)
Gletz✔✔Dutch term for a feather in a diamond. (Assignment 9)
,Kaps✔✔Dutch term for a diamond that has been cleaved, split, or sawn, but not
fashioned. (Assignment 9)
1380✔✔the first polished diamonds appeared in Europe around
adamantine✔✔The highest degree of luster possible in a transparent material.
Incidence✔✔the angle at which a ray of light strikes a surface, measured from the
normal
critical angle✔✔Angle between the normal and the maximum angle of refraction,
which is the largest angle at which ray inside the diamond can escape
Refractive Index (RI)✔✔A MEASURE of the change in the speed and angle of light
as it passes from one material to another.
critical angle✔✔Light rays that enter at the maximum angle of refraction form a
_____________ cone inside the diamond
RI✔✔The higher a gems _____, the smaller its critical angle
crown✔✔A properly proportioned pavilion controls the way light travels through a
diamond and forces it to exit through the ______, giving the diamond maximum
brightness
outside✔✔When light strikes _______ the critical angle cone, it reflects back into the
diamond. This is called total reflection.
small✔✔A ______ critical angle gives light less opportunity to exit. Reason why well-
cut diamonds can be so bright
Glide plane✔✔Crystal distortion caused during growth when one part of the lattice is
offset in relation to the rest
Graining (Grain Lines)✔✔visible, shadow-like lines in a diamond caused by
irregularities in the crystal structure
tetrahedron✔✔In diamond, a group of five carbon atoms with one at the center
✔✔
cleavage plane✔✔plane parallel to a possible crystal face; where a diamond can
split cleanly when struck
covalent bond✔✔a chemical bond formed by two atoms sharing electrons
,crystal✔✔SOLID MATTER with atoms arranged in a regular, repeating pattern
crystalline✔✔composed of crystals or related to crystals
crystal planes✔✔internal directions parallel to a minerals unit cell surfaces
crystal shape (form)✔✔geometric shape of a well formed crystal
crystal structure (lattice)✔✔regular, repeating ARRANGEMENT of atoms in a
mineral
crystal systems✔✔categories of crystals based on their symmetry and internal
structure
Doubling✔✔the appearance of double images of a gemstone's facet junctions on the
side opposite the viewer
Doubly refractive (anisotropic)✔✔Possessing different physical or optical properties
in different crystal directions
Glassie✔✔a well shaped, transparent, octahedral diamond crystal with sharp,
square edges
Glide plane✔✔Crystal distortion caused during growth when one part of the lattice is
offset in relation to the rest
graining (grain lines)✔✔visible, shadow-like lines in a diamond caused by
irregularities in the crystal structure
habit✔✔characteristic crystal shape of a specific mineral
macle✔✔a flat, triangular twinned diamond crystal
octahedron✔✔A form with eight equal triangular faces.
Singly refractive (isotropic)✔✔possessing the same physical or optical properties in
all crystal directions
specific gravity (SG)✔✔ratio of the weight of a material to that of an equal volume of
water
tetrahedron✔✔in diamond, a group of five carbon atoms with one at the center
thermal conductivity✔✔the relative ability of a material to transfer heat
thermal expansion✔✔capacity of a material to expand when its heated
, trace elements✔✔Atoms in a gem that aren't part of its essential chemical
composition.
Twinned crystal✔✔Crystal consisting of two or more
intergrown crystals with opposing crystal directions.
unit cell✔✔smallest group of atoms with the characteristic chemical composition and
the basic crystal structure of a mineral
craftsmanship✔✔The care that goes into the fashioning of a polished diamond, as
confirmed by its finish. (Assignment 15)
Culet size✔✔The size of the facet at the bottom of the diamond where the pavilion
mains meet. (Assignment 15)
design✔✔a diamond's physical shape, including its proportions and durability,
determined by decisions made during the fashioning process
finish✔✔the quality of the polish and precision of the cut of a fashioned gemstone
girdle thickness percentage✔✔Girdle thickness expressed as a percentage of
average girdle diameter. (Assignment 15)
Lower half length percentage✔✔the length of the lower half facets expressed as a
percentage of the total distance between the girdle and the culet
pavilion angle✔✔The angle formed by the pavilion mains and the girdle plane.
Pavilion depth percentage✔✔The distance from the girdle plane to the culet,
expressed as a percentage of average girdle diameter. (Assignment 15)
38°✔✔If a diamond's pavilion depth percentage is 39.0 percent with no culet facet,
its pavilion angle is approximately
larger✔✔As a diamond's pavilion gets deeper, its table reflection becomes
a black spot under the table✔✔If a diamond's culet is too large, it will look like
37.0%✔✔which of the following pavilion depth percentages would most likely cause
the girdle reflection to be visible face-up through the table?
-37.0%
-42.0%
-45.0%
-48.0%
craftsmanship✔✔the care that goes into the fashioning of a polished diamond, as
confirmed by its finish, is its
questions and answers
Aggregate✔✔A solid mass of individual, randomly oriented crystals, intergrown, or
held together by a natural binding agent.
Fair✔✔Total depth percentage between 51% to 70.9%
Naif✔✔The natural unpolished surface of a rough diamond
Point Naif✔✔A seventeenth-century term for a diamond octahedron or other crystal
shape on which the natural faces are apparent. (Assignment 9)
Bast✔✔Frosted rough diamond. "Bark" in Dutch. (Assignment 9)
Cross Working✔✔Placing the bezel and pavilion facets on round and fancy shapes.
Sometimes combined with blocking, especially on smaller stones. Also called cross
cutting. (Assignment 9)
Foss✔✔Irregular furrow or groove in the surface of a diamond, characteristic of
diamond crystals in the gray color range. (Assignment 9)
Sharp✔✔A small diamond with a sharp edge, cemented into a dop and used to kerf
another diamond in preparation for cleaving.
Or, a small diamond used to brute diamonds or round up a girdle in the final stages
of polishing.
Three point diamond✔✔A diamond with its table nearly parallel to a possible
octahedral face. (Assignment 9)
Twisted Stone✔✔A diamond with grain layers that are not on parallel planes, or one
with partial twinning. (Assignment 9)
Twisting✔✔A blocking technique in which the diamond is turned to position the
softest polishing direction against the polishing wheel. (Assignment 9)
Two point diamond✔✔A diamond on which the table has been polished parallel to a
dodecahedral plane. (Assignment 9)
Water✔✔A historic term once used in Europe to describe either the color or the
transparency of a diamond
Four point diamond✔✔A diamond with the table parallel to a possible cubic face.
(Assignment 9)
Gletz✔✔Dutch term for a feather in a diamond. (Assignment 9)
,Kaps✔✔Dutch term for a diamond that has been cleaved, split, or sawn, but not
fashioned. (Assignment 9)
1380✔✔the first polished diamonds appeared in Europe around
adamantine✔✔The highest degree of luster possible in a transparent material.
Incidence✔✔the angle at which a ray of light strikes a surface, measured from the
normal
critical angle✔✔Angle between the normal and the maximum angle of refraction,
which is the largest angle at which ray inside the diamond can escape
Refractive Index (RI)✔✔A MEASURE of the change in the speed and angle of light
as it passes from one material to another.
critical angle✔✔Light rays that enter at the maximum angle of refraction form a
_____________ cone inside the diamond
RI✔✔The higher a gems _____, the smaller its critical angle
crown✔✔A properly proportioned pavilion controls the way light travels through a
diamond and forces it to exit through the ______, giving the diamond maximum
brightness
outside✔✔When light strikes _______ the critical angle cone, it reflects back into the
diamond. This is called total reflection.
small✔✔A ______ critical angle gives light less opportunity to exit. Reason why well-
cut diamonds can be so bright
Glide plane✔✔Crystal distortion caused during growth when one part of the lattice is
offset in relation to the rest
Graining (Grain Lines)✔✔visible, shadow-like lines in a diamond caused by
irregularities in the crystal structure
tetrahedron✔✔In diamond, a group of five carbon atoms with one at the center
✔✔
cleavage plane✔✔plane parallel to a possible crystal face; where a diamond can
split cleanly when struck
covalent bond✔✔a chemical bond formed by two atoms sharing electrons
,crystal✔✔SOLID MATTER with atoms arranged in a regular, repeating pattern
crystalline✔✔composed of crystals or related to crystals
crystal planes✔✔internal directions parallel to a minerals unit cell surfaces
crystal shape (form)✔✔geometric shape of a well formed crystal
crystal structure (lattice)✔✔regular, repeating ARRANGEMENT of atoms in a
mineral
crystal systems✔✔categories of crystals based on their symmetry and internal
structure
Doubling✔✔the appearance of double images of a gemstone's facet junctions on the
side opposite the viewer
Doubly refractive (anisotropic)✔✔Possessing different physical or optical properties
in different crystal directions
Glassie✔✔a well shaped, transparent, octahedral diamond crystal with sharp,
square edges
Glide plane✔✔Crystal distortion caused during growth when one part of the lattice is
offset in relation to the rest
graining (grain lines)✔✔visible, shadow-like lines in a diamond caused by
irregularities in the crystal structure
habit✔✔characteristic crystal shape of a specific mineral
macle✔✔a flat, triangular twinned diamond crystal
octahedron✔✔A form with eight equal triangular faces.
Singly refractive (isotropic)✔✔possessing the same physical or optical properties in
all crystal directions
specific gravity (SG)✔✔ratio of the weight of a material to that of an equal volume of
water
tetrahedron✔✔in diamond, a group of five carbon atoms with one at the center
thermal conductivity✔✔the relative ability of a material to transfer heat
thermal expansion✔✔capacity of a material to expand when its heated
, trace elements✔✔Atoms in a gem that aren't part of its essential chemical
composition.
Twinned crystal✔✔Crystal consisting of two or more
intergrown crystals with opposing crystal directions.
unit cell✔✔smallest group of atoms with the characteristic chemical composition and
the basic crystal structure of a mineral
craftsmanship✔✔The care that goes into the fashioning of a polished diamond, as
confirmed by its finish. (Assignment 15)
Culet size✔✔The size of the facet at the bottom of the diamond where the pavilion
mains meet. (Assignment 15)
design✔✔a diamond's physical shape, including its proportions and durability,
determined by decisions made during the fashioning process
finish✔✔the quality of the polish and precision of the cut of a fashioned gemstone
girdle thickness percentage✔✔Girdle thickness expressed as a percentage of
average girdle diameter. (Assignment 15)
Lower half length percentage✔✔the length of the lower half facets expressed as a
percentage of the total distance between the girdle and the culet
pavilion angle✔✔The angle formed by the pavilion mains and the girdle plane.
Pavilion depth percentage✔✔The distance from the girdle plane to the culet,
expressed as a percentage of average girdle diameter. (Assignment 15)
38°✔✔If a diamond's pavilion depth percentage is 39.0 percent with no culet facet,
its pavilion angle is approximately
larger✔✔As a diamond's pavilion gets deeper, its table reflection becomes
a black spot under the table✔✔If a diamond's culet is too large, it will look like
37.0%✔✔which of the following pavilion depth percentages would most likely cause
the girdle reflection to be visible face-up through the table?
-37.0%
-42.0%
-45.0%
-48.0%
craftsmanship✔✔the care that goes into the fashioning of a polished diamond, as
confirmed by its finish, is its
