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Citrine is a macrocrystalline variety of the mineral quartz, characterized by its transparent yellow, orange, or brownish-orange coloration. It belongs to the trigonal crystal system and typically forms in prismatic crystals with pyramidal terminations. Its hardness of 7 on the Mohs scale makes it suitable for everyday wear in jewelry. Natural citrine is relatively rare, with most commercial citrine being heat-treated amethyst or smoky quartz. The color intensity can range from pale yellow to deep reddish-orange, with the deeper, more saturated colors often being more highly valued.
How to Identify
- Color
- Ranges from pale yellow to golden yellow, orange-yellow, and reddish-brown. Natural citrine tends to be paler, while heat-treated amethyst often exhibits more intense orange to reddish-orange hues, sometimes with a reddish tint at the tips.
- Luster
- Vitreous (glassy).
- Texture
- Smooth to conchoidal fracture surfaces when broken. Crystal faces are typically smooth.
- Crystal Form
- Typically forms as hexagonal prisms terminated by rhombohedral faces. Can also be found as massive or granular aggregates. Often found as geode linings or in vugs.
- Cleavage
- None. Quartz exhibits no true cleavage.
- Geological Environment
- Found in igneous rocks (especially granites and pegmatites), metamorphic rocks, and hydrothermal veins. Also occurs in alluvial deposits as detrital grains due to its hardness and resistance to weathering.
Key Facts
- Hardness: 7 (Mohs scale)
- Specific Gravity: 2.65 g/cm³
- Crystal System: Trigonal
- Color: Yellow, golden-yellow, orange-yellow, reddish-brown
- Luster: Vitreous
- Transparency: Transparent to translucent
- Fracture: Conchoidal
- Cleavage: None
- Composition: Silicon dioxide (SiO2) with trace iron impurities (Fe3+)
Quick Check
- Color: Yellow to orange-brown
- Luster: Vitreous (glassy)
- Streak: White
Physical Characteristics
- Crystal Habit: Prismatic, often terminated by rhombohedral faces; also massive, granular, cryptocrystalline (chalcedony variety).
- Cleavage Type: None (absence of cleavage planes)
- Fracture Type: Conchoidal (shell-like, curved fractures)
- Tenacity: Brittle
- Luster Type: Vitreous (glassy)
Formation
Natural citrine forms primarily in igneous and metamorphic rocks. It crystallizes from hydrothermal solutions in veins and geodes, often associated with granitic pegmatites. The characteristic yellow to orange-brown color is due to trace amounts of iron impurities (Fe3+) within the quartz crystal lattice. This coloration can be natural or induced by heat treatment of amethyst or smoky quartz. When amethyst (purple quartz) or smoky quartz (brown to black quartz) containing iron impurities is heated to temperatures between 400-560 °C, the iron oxidation state changes, resulting in the yellow to orange hues of citrine. Most commercially available citrine is heat-treated amethyst.
Usage
Citrine is primarily used as a gemstone in jewelry due to its attractive color and durability. It is cut into various shapes for rings, necklaces, earrings, and bracelets. Larger specimens are also used for ornamental carvings and as collector's items. Historically, it has been used for decorative purposes and believed to possess various metaphysical properties.
Age Distribution
Citrine, as a variety of quartz, can form in geological environments spanning billions of years, from Precambrian to Cenozoic. Its formation is tied to the crystallization of silica-rich magmas, hydrothermal activity, and metamorphic processes.
Where to Find
Brazil
The primary source of both natural and heat-treated citrine, particularly from the states of Rio Grande do Sul and Minas Gerais. Many large geodes of amethyst are found here and subsequently heat-treated to produce citrine.
Madagascar
Known for producing natural citrine, often with a desirable golden-orange color.
Uruguay
Another significant source of amethyst that is often heat-treated into citrine.
Russia (Ural Mountains)
Historically a source of natural citrine.
Spain
Some natural citrine deposits are found here.
France
Minor occurrences of natural citrine.
Scotland
Historically known for 'Cairngorm' quartz, which can include smoky quartz and some citrine.
Finding Tips
Look for Quartz Environments
Search in areas known for quartz deposits, such as pegmatites, hydrothermal veins, and areas with granitic intrusions. Geodes and vugs in volcanic rocks can also host citrine.
Identify Associated Minerals
Citrine often occurs with other quartz varieties (amethyst, smoky quartz), feldspars, micas, and tourmaline in pegmatitic environments.
Check for Color Consistency
Natural citrine often has a more muted, even color distribution. Heat-treated amethyst-turned-citrine may show a more intense, sometimes reddish-orange color, often with a white base where the original amethyst crystal grew from.
Hardness Test (with caution)
Citrine will scratch glass and steel (Mohs 7). This helps distinguish it from softer yellow minerals, but be careful not to damage the specimen.
Observe Crystal Habit
Look for characteristic hexagonal prismatic crystals with pyramidal terminations, either as individual crystals or in clusters within vugs.
Similar Rocks
Yellow Topaz
Topaz (Al2SiO4(F,OH)2)
Also known as: Imperial Topaz (for specific colors)
Smoky Quartz
Quartz (SiO2) variety Smoky Quartz
Also known as: Morion (dark variety)
Amethyst
Quartz (SiO2) variety Amethyst
Also known as: Purple Quartz
Yellow Sapphire
Corundum (Al2O3) variety Yellow Sapphire
Also known as: Pukhraj
Scientific Classification
- Mineral Class
- Silicates
- Group
- Tectosilicates (Quartz Group)
- Crystal System
- Trigonal (or Hexagonal-Rhombohedral)
- Chemical Formula
- SiO2
- Composition
- Silicon dioxide
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