Radiating
It is an aggregate which is composed of tiny and slender crystals bonded together radiating from a central point. The radiation of such can either be flat or three dimensional. If it is three dimensional, the aggregate usually occurs with circular, ball-like masses, and is known as spherulitic.

Radiation
It is a term for the emission of alpha, beta, or gamma rays.

Radical
It is the compounds acting as a single atom when combined with other elements to form minerals. It contains one or more unpaired electrons.

Radioactive
It is a term given to describe substances containing stoms with unstable nuclei. It causes the substance to decay slowly and emit radiation. If kept in proper settings, radioactive minerals take an extremely long time to decay.

Radioactivity
It is the effect of radioactive material, which emits alpha, beta, and gamma rays.

Rare earth elements
It is a group of elements which are similar in chemical properties and were once thought to be extremely rare. These elements take up numbers 57 through 71 on the periodical table and are also known as the 'lanthanides.'

Reflection
When a light hits a material and then bounces off, it is called as reflection. The degree and angel of the reflection depends upon the surface, which can be smooth, flat, polished. A polished hematite is a good example which defines a reflective mineral. In certain cases, it even produces a mirror-like reflection.

Refraction
It is the bending of white light when it enters a new dimension, like air to water or from air to crystal, and thereafter the white light splits into the colors of the spectrum.

Refractive index
It is the amount of refraction taking place in a particular substance which is directly co-related to the speed of light in that substance. The refractive index is directly related to the amount of dispersion that further increases the brilliance of a material. Refractive indices are measured with a refractometer.

Refractive indices
It is the plural form of refractive index.

Refractometer
It is the instrument for measuring the refraction of light entering through a different dimension, like from air to water or from air into a crystal.

Refractory ore
It is ore from which extraction of valuable constituents is very difficult. It may require special treatments, like pressure leaching, to extract the valuable minerals.

Resistance
It is the unyielding of a material to a destructive acids and of tough environments.

Rhombohedron
It is a term given to a six sided polyhedron with each side shaped as a rhombus.

Rift
It is a crack in a rock. In broader way it generally refers to the separation of plates on fault areas, forming a depression in the earth.

Rock
It is a term for an indefinite mixture of naturally occurring substances, mostly minerals. The composition may vary in containment of minerals and organic substances, and they are never exact.

Rock Crystal
It is a name given to transparent, colorless, crystal of quartz.

Room and Pillar mining
It is the common mining method which is most suitable for thick, flat lying, laterally homogeneous, ore bodies. The pillars of the ore are left behind after the mining to support the hanging wall. It is also known as Pillar and Stall mining.