| Diagenesis
transformation of natural materials at low
temperatures
Diatom
minute marine or fresh water species with
silica skeletons
Diatomite
soft white deposits composed of diatom skeletons
Diffraction
breaking up of light by a regular structure
Dolerite
an igneous rock of similar composition to
basalt, silica content about 50%.
Doublet
in jewellery, a slice of precious stone,
such as opal, with a backing of glass or
other material
Dugout
in the opal fields, an underground dwelling
Duricrust
hard surface layer sometimes formed in dry
areas by silicification |
