Minerals displaying the lustre of resin or of smooth-surfaced plastic are described as resinous. Amber, for example, has resinous lustre.
When viewed under plane polarised light, some mineral grains are more clearly defined than others. They have heavier, darker edges. These minerals have higher relief.
Relief is determined by the difference in the refractive indices of the grain and mounting medium. The mounting medium typically has a refractive index (R.I., ni) of ~1.54. A mineral with a low refractive index, such as quartz (R.I., ni ~1.5) has low relief because it has a refractive index very similar to that of the mounting medium. A mineral with a high refractive index, such as garnet (R.I., ni ~1.7) has high relief because it has a refractive index much higher than that of the mounting medium.
Compare with phenocryst.
A porphyroblast is the metamorphic equivalent of a phenocryst. Do not confuse them! It is a large crystal set into a finer-grained fabric, in a metamorphic rock.
Compare with phenocryst.
An igneous rock containing phenocrysts in a fine-grained groundmass is said to have a porphyritic texture.
Compare with permeability.
The proportion of the material occupied by space, measured in volume percent. A porous material contains fluid-filled spaces, or pores, while a non-porous material does not. NB, make sure you understand the difference between porosity and permeability.
Compare with permeability.
A crystalline sample of a single mineral, containing many crystals. Quartzite, for example, is polycrystalline quartz.