- Citrine (Natural)
- Mounted on Wooden Base
- Found in Brazil
- Specimen measures approx. 6 1/4″ tall with stand
Citrine is the yellow to brownish-red variety of the mineral Quartz. It is a widely used as a gemstone, and after Amethyst it is the most popular Quartz gem. Most Citrine is formed by heat treating purple Amethyst. Citrine may also be produced by heat-treating Smoky Quartz from certain localities. In some Amethyst deposits, the Amethyst has been partially or fully changed over to yellow Citrine by natural means of heating.
Natural Citrine, which is rare, is yellow to orange-yellow, and occurs in much lighter hues than the heat-treated material, which is dark orange-brown to reddish-brown. Virtually all heat-treated material has a reddish tint, whereas the natural specimens do not. Natural light yellow Citrine is often called “Lemon Quartz” on the gemstone market. Sometimes Citrine has a “smoky” hue to it, and can be borderlined between Citrine and Smoky Quartz, with either definition being correct.
A mineral is a naturally occurring chemical compound. Most often, they are crystalline and abiogenic in origin. A mineral is different from a rock, which can be an aggregate of minerals or non-minerals and does not have one specific chemical composition, as a mineral does. The exact definition of a mineral is under debate, especially with respect to the requirement that a valid species be abiogenic, and to a lesser extent with regard to it having an ordered atomic structure.
The study of minerals is called mineralogy. There are over 5,300 known mineral species; over 5,070 of these have been approved by the International Mineralogical Association (IMA). The silicate minerals compose over 90% of the Earth’s crust. The diversity and abundance of mineral species is controlled by the Earth’s chemistry. Silicon and oxygen constitute approximately 75% of the Earth’s crust, which translates directly into the predominance of silicate minerals.
Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, which were determined by the mineral’s geological environment when formed. Changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals.
Minerals can be described by their various physical properties, which are related to their chemical structure and composition. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, and specific gravity. More specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid.
Minerals are classified by key chemical constituents; the two dominant systems are the Dana classification and the Strunz classification. The silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a base unit of a [SiO4]4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions, which gives the shape of a tetrahedron. These tetrahedra can be polymerized to give the subclasses: orthosilicates (no polymerization, thus single tetrahedra), disilicates (two tetrahedra bonded together), cyclosilicates (rings of tetrahedra), inosilicates (chains of tetrahedra), phyllosilicates (sheets of tetrahedra), and tectosilicates (three-dimensional network of tetrahedra). Other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates.