Decomposition
It is the molecular breakdown of certain materials that causes a mineral to disintegrate.

Decrepitation
It is a term used for an explosives shattering of minerals. Generally it is done through tube tests or the blowpipe tests.

Dehydration
It is a term for the removal of water from a substance. There are many minerals which loses water in their structure naturally at normal conditions, and it transforms into another mineral. For example a torbernite transforms to meta-torbernite.

Deposit
It is an accumulation of minerals within a rock formation.

Detritus
It is when the rock fragments or minerals on the Earth's surface erodes by natural causes, ending up to a different region. For example: Downstream currents.

Development
It is a phase of activity which ranges from confirmation of a mineral deposit to the decision of building a mine. The development includes all the geological, engineering and economic work which are necessary to ensure profitable mining and compliance with applicable laws.

Devitrification
It is a term used for the changing over of a mineral with a crystalline structure from a natural glass.

Devonian
It is the geological period which is 417 to 354 million years ago.

Diagenesis
It is the last stage of the changing over to sedimentary rock from sediment.

Diamagnetism
It is the magnetic property of a mineral that causes it to be repelled from magnetic fields.

Diaphaneity
It is the "see-through" quality of a substance. In regard to minerals, it is variable with transparency.

Diaphanous
It is a term used for the ability to be seen through, either transparent or translucent.

Dichroic
Minerals which exhibit dichroism are said such.

Dichroism
It literally means "two colors." A mineral displaying different color from different angle while viewing such is said to display dichroism.

Diffraction
When from one medium to another, the light bends after entering, it is said such. For example the bending of light from air to water.

Dike
It is a term given to the wall of igneous rock which cuts across layers of surrounding rock.

Dodecahedron
It is a term given to twelve sided polyhedron where all the sides are equidimensional and either rhombic or pentagonal. If composed of rhombs, is known as a rhombic dodecahedron or just dodecahedron and known as pentagonal dodecahedron if composed of pentagons. Minerals shaped such belongs to the isometric system.

Dollar
It is a flat, spherical disc of radiating crystals. It is also a variety of Pyrite/Marcasite.

Dolomite
It is a common rock forming mineral and is comprised of calcium, carbon, magnesium and oxygen - CaMg(CO₃).

Double refraction
It is a term given to the phenomenon which is exhibited on all non-opaque minerals, leaving amorphous ones and those that crystallize in the isometric system. When a ray of light enters the crystal, it splits up into two separate rays and makes everything observed through the crystal appear as double. In many minerals it is very weak and is observed only through special instruments but in some minerals like Iceland Spar variety of Calcite is strongly visible. Double refraction differs from mineral to mineral. This property is used in identifying gems. It is measured with a refractometer.

Drift (tunnel)
It is the underground passage which provides access to the mining operarions.

Druse
It is a cavity in a mineral or a rock which is filled with protruding crystals. It can be completely or partially filled with crystals.