Assignment 5 - The Diamond Crystal Flashcards
Solid matter with atoms arranged in a regular, repeating order
Crystal
Composed of crystals or related to crystals
Crystalline
The basic structural unit of all matter.
Atom
How do carbon atoms combine to build a diamond crystal?
Neighbouring atoms share electrons and form a “covalent bond”. Covalent bonds are the strongest of all atomic bonds. Diamond’s atoms are more closely bonded than the atoms of any other natural element.
What is a diamond’s characteristic crystal shape?
The most common habit of a gem diamond is the octahedron, but perfectly shaped octahedral rough is rare.
A chemical bond formed by two atoms sharing electrons
Covalent Bond
In a diamond, a group of five carbon atoms with one at the center.
Tetrahedron
Smallest group of atoms with the characteristic composition and the basic crystal structure of a mineral.
Unit cell
Geometric shape of a well-formed crystal
Crystal shape (form)
Characteristic crystal shape of a specific mineral
Habit
A form with eight equal triangular faces.
Octahedron
A well-shaped, transparent, octahedral diamond crystal with sharp, square edges.
Glassie
Regular, repeating arrangement of atoms in a mineral
Crystal structure (lattice)
Categories of crystals based on their symmetry and internal structure.
Crystal systems
Which crystal system does Diamond form in?
Cubic.
What is the specific gravity of a diamond?
3.52
Possessing the same physical or optical properties in all crystal directions
Singly refractive (isotropic)
Possessing different physical or optical properties in different crystal directions
Doubly refractive (anisotropics)
The appearance of double images of a gemstone’s facet junction on the side opposite the viewer
Doubling
An imperfection or deviation from the ideal crystal lattice
Defect
What are the categories of crystal lattice defects in a diamond crystal?
The three categories of defects are:
- point (intrinsic & extrinsic)
- line
- volume
Defect in relation to a single atom in the crystal lattice.
Point defect.
A (intrinsic) point defect when an atom is missing from it original position in the lattice.
Vacancy.
Atoms in a gem that aren’t part of its essential chemical composition
Trace elements.
Defect in relation to a line in the crystal lattice
Line defect
The force required to produce distortion in the crystal lattice
Stress
The plane or surface in which a dislocation travels through the crystal to cause an offset
Glide plane
Defects caused by a three-dimensional aggregate of atoms or vacancies within the crystal lattice
Volume defect.
Distortion or deformation in a crystal
Strain
Visible, shadow-like lines in a diamond caused by irregularities in the crystal structure.
Graining (grain lines)
How do dislocations contribute to strain in a diamond crystal?
The more dislocations that occur in a crystal, the more strain the crystal bears.
What is the foundation of the diamond type classification system?
The presence or absence of nitrogen and boron atoms and the way they are arranged in the crystal lattice.
What diamond types are rarely found in nature?
Type Ib (with isolated nitrogen imppurities). Most are Ia.
How does a diamond’s crystal structure dictate cutting methods?
The cleavage planes (cubic, octahedral, dodecahedral) are the most important directions to a diamond cutter.
What are diamond’s basic crystal shapes and planes?
- Cubic
- Octahedral
- Dodecahedral
How is diamond rough evaluated for cutting?
Diamond rough’s potential as a faceted gem depends on its shape, clarity and color.
Shape is the most important factor in a rough gem diamond crystal’s potential value.
Inclusions can limit a rough diamond’s potential shape.
Capacity of a material to expand when it’s heated
Thermal expansion
The relative ability of a material to transfer heat
Thermal conductivity
Plane parallel to a possible crystal face, where a diamond can split clearly when struck.
Cleavage plane
Crystal consisting of two or more intergrown crystals with opposing crystal directions.
Twinned crystal
A flat, triangular twinned diamond crystal.
Macle
A solid mass of individual, randomly oriented crystals, inter-grown and held together by a natural binding agent.
Aggregate
How are nitrogen atoms arranged in the diamond crystal lattice when diamonds first form?
Isolated.
What is the only way to accurately determine diamond type?
Spectroscopy
How many directions of cleavage does diamond have?
Four.
Which type of growth mark indicates an octahedral crystal face in diamond?
Trigons.
What can cause a combination of octahedral and dodecahedral crystal forms?
Resorption
The process in which the outer surface of a diamond is partially dissolved during transport.
Resorption
What is the most important value factor for cuttable rough diamond?
Shape
What is a shallow diamond crystal with limited potential shape?
Flat
How many tetrahedrons form the core of a diamond’s unit cell?
4
How do you distinguish Type I from Type II diamonds
Type I contains Nitrogen impurities.
Type II do not contain significant Nitrogen impurities.
How do you distinguish Type Ia from Type Ib diamonds?
Both have Nitrogen impurities.
Type Ia have aggregated Nitrogen impurities. (a=aggregate)
Type Ib have isolated Nitrogen impurities.
How do you distinguish Type IIa from Type IIb Diamonds
Type IIb diamonds contain Boron impurities. (b = boron)
What is another name for the cubic system?
Isometric
