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Red Quartz, specifically Hematoid Quartz, is a variety of macrocrystalline quartz characterized by its distinctive red, orange, or reddish-brown coloration. This color is not inherent to the quartz itself but is caused by microscopic inclusions of iron oxides, predominantly hematite (Fe2O3) and sometimes goethite (FeO(OH)). These inclusions can be uniformly distributed, creating a solid red appearance, or they can form distinct patterns, layers, or 'phantoms' within the quartz crystal, often highlighting growth stages. The intensity and hue of the red color can vary significantly depending on the concentration and type of iron oxide present. It shares all the fundamental physical and chemical properties of quartz, with the added aesthetic appeal of its iron oxide inclusions.
How to Identify
- Color
- Ranges from pale pinkish-red to deep brick red, orange-red, or reddish-brown. The color is due to iron oxide inclusions, often appearing as specks, clouds, or distinct phantoms within the transparent to translucent quartz.
- Luster
- Vitreous (glassy) on crystal faces and fracture surfaces.
- Texture
- Smooth to slightly granular, depending on the crystal habit and presence of inclusions. Often exhibits a conchoidal fracture.
- Crystal Form
- Typically forms hexagonal prisms terminated by hexagonal pyramids. Can also be massive, granular, or drusy. Inclusions often highlight growth zones.
- Cleavage
- None. Quartz lacks cleavage.
- Geological Environment
- Found in hydrothermal veins, pegmatites, and metamorphic rocks. It forms in environments where silica-rich fluids are present alongside iron-bearing minerals, allowing for the co-precipitation or inclusion of iron oxides during quartz crystallization.
Key Facts
- Hardness: 7 on the Mohs scale
- Specific Gravity: 2.65 g/cm³ (for pure quartz; inclusions may slightly alter this)
- Crystal System: Trigonal
- Color: Red, orange-red, reddish-brown (due to hematite/goethite inclusions)
- Luster: Vitreous
- Transparency: Transparent to translucent, opaque if inclusions are dense
- Fracture: Conchoidal
- Cleavage: None
- Composition: Silicon dioxide (SiO2) with iron oxide (Fe2O3, FeO(OH)) inclusions
Quick Check
- Color: Red, orange-red, reddish-brown (due to iron oxide inclusions)
- Luster: Vitreous (glassy)
- Streak: White (for quartz itself); reddish-brown if significant hematite inclusions are rubbed off, but typically tested on a clean quartz surface.
Physical Characteristics
- Crystal Habit: Prismatic, often terminated by rhombohedral faces; also massive, granular, cryptocrystalline.
- Cleavage Type: Absent
- Fracture Type: Conchoidal
- Tenacity: Brittle
- Luster Type: Vitreous
Formation
Hematoid Quartz forms in hydrothermal veins, pegmatites, and other igneous and metamorphic environments where silica-rich fluids interact with iron-bearing minerals. The red coloration is due to inclusions of iron oxides, primarily hematite (Fe2O3) or goethite (FeO(OH)), which are deposited during the crystal growth of quartz. These iron oxides can be present as fine particles, coatings, or phantoms within the quartz crystals.
Usage
Primarily used as an ornamental stone, for lapidary purposes (cabochons, spheres, carvings), and in jewelry. It is also popular among mineral collectors and in metaphysical practices.
Age Distribution
Geologically widespread, found in formations ranging from Precambrian to Cenozoic, depending on the host rock and hydrothermal activity.
Where to Find
Brazil
Minas Gerais is a significant source, known for producing high-quality Hematoid Quartz with vibrant red and orange inclusions.
Madagascar
Produces various forms of quartz, including those with iron oxide inclusions, often exhibiting interesting patterns.
United States
Localities in Arkansas and other states can yield quartz with iron staining or inclusions, though often less intensely colored than Brazilian material.
South Africa
Known for some occurrences of quartz with hematite inclusions.
China
Various quartz deposits, some of which contain iron oxide inclusions.
Finding Tips
Look for Hydrothermal Veins
Hematoid Quartz is commonly found in quartz veins that have undergone hydrothermal alteration, often associated with igneous or metamorphic activity. Look for areas with exposed vein systems.
Identify Iron Staining
The presence of reddish-brown staining on surrounding rocks or within quartz specimens can indicate the presence of iron oxides, which are responsible for the color of Hematoid Quartz.
Examine Crystal Habits
Search for well-formed hexagonal quartz crystals. The iron oxide inclusions may be visible as distinct layers or phantoms within the crystal, indicating growth stages.
Check for Associated Minerals
Hematoid Quartz can be found alongside other minerals typical of hydrothermal environments, such as feldspar, mica, and various sulfide minerals (though the latter are not directly responsible for the red color).
Safety Precautions
When collecting in the field, always wear appropriate safety gear, including eye protection and gloves. Be aware of unstable rock formations and potential hazards in mining or quarrying areas. While quartz itself is not acutely toxic, prolonged inhalation of fine silica dust (e.g., from cutting or grinding) can lead to silicosis, a serious lung disease. Always use proper ventilation and respiratory protection when working with quartz.
Similar Rocks
Jasper
SiO2 (with iron oxide inclusions)
Also known as: Red Jasper
Carnelian
SiO2 (with iron oxide impurities)
Also known as: Cornelian
Rutile Quartz
Quartz (SiO2) with Rutile (TiO2) inclusions
Also known as: Rutilated Quartz
Strawberry Quartz
Quartz (SiO2) with Lepidocrocite or Hematite inclusions
Also known as: Scarlet Quartz
Scientific Classification
- Mineral Class
- Silicate (Tectosilicate)
- Group
- Quartz Group
- Crystal System
- Trigonal
- Chemical Formula
- SiO2 (with Fe2O3 and/or FeO(OH) inclusions)
- Composition
- Silicon dioxide with iron oxide inclusions
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