Hematoid Quartz

Description

Hematoid Quartz is a variety of macrocrystalline quartz (SiO2) that contains inclusions of hematite (Fe2O3). These inclusions are responsible for its distinctive coloration, which can range from pale yellow, orange, and red to reddish-brown. The distribution of hematite can be uniform, creating a cloudy or diffused color, or concentrated in phantoms, layers, or speckles within the quartz crystal. The quartz itself is typically colorless or milky, with the iron oxide inclusions providing the vibrant hues. The term 'Hematoid' refers to the presence of hematite, distinguishing it from other iron-stained quartz varieties where the iron oxides might be limonite or goethite.

How to Identify

Color

Ranges from pale yellow, orange, and red to reddish-brown, often with distinct patterns or phantoms caused by hematite inclusions. The base quartz can be clear or milky.

Luster

Vitreous (glassy) for the quartz, with metallic to dull luster for visible hematite inclusions.

Texture

Smooth to slightly rough depending on the crystal faces and the nature of the inclusions. Can be granular in massive forms.

Crystal Form

Typically occurs as prismatic hexagonal crystals, often terminated, or as massive, granular aggregates. Inclusions can form phantoms or layers within the crystal.

Cleavage

None (conchoidal fracture).

Geological Environment

Hydrothermal veins, pegmatites, and sedimentary environments where silica-rich fluids interact with iron-rich solutions. Often found in association with other quartz varieties, feldspars, and various iron minerals.

Key Facts

• Hardness: 7 on the Mohs scale (for quartz)
• Specific Gravity: 2.65 - 2.69 (for quartz, slightly higher with dense hematite inclusions)
• Crystal System: Trigonal
• Color: Colorless to milky white quartz with yellow, orange, red, or reddish-brown hematite inclusions.
• Luster: Vitreous
• Transparency: Transparent to translucent, opaque if inclusions are very dense.
• Fracture: Conchoidal
• Cleavage: None
• Composition: Silicon dioxide (SiO2) with iron oxide (Fe2O3) inclusions.

Quick Check

• Color: Yellow, orange, red, reddish-brown (due to hematite inclusions)
• Luster: Vitreous (glassy)
• Streak: White (for quartz), reddish-brown (if hematite is rubbed directly on a streak plate, but typically not practical for inclusions)

Physical Characteristics

• Crystal Habit: Prismatic hexagonal crystals, often terminated; also massive, granular, or cryptocrystalline aggregates.
• Cleavage Type: Absent
• Fracture Type: Conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous

Formation

Hematoid Quartz forms when quartz crystals grow in an environment rich in iron oxides, specifically hematite (Fe2O3). The hematite can be present as microscopic particles, thin films, or larger inclusions within or on the surface of the quartz crystal. This typically occurs in hydrothermal veins, pegmatites, or sedimentary environments where iron-rich fluids interact with silica-rich solutions during crystal growth. The iron oxides can precipitate simultaneously with the quartz or coat pre-existing 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 due to its aesthetic appeal. Historically, quartz varieties have been used in various applications, but Hematoid Quartz's specific coloration makes it desirable for decorative uses.

Age Distribution

Found in geological formations ranging from Precambrian to Cenozoic, depending on the host rock and hydrothermal activity.

Where to Find

Finding Tips

Similar Rocks

Scientific Classification

Mineral Class

Silicates

Group

Tectosilicates (Quartz Group)

Crystal System

Trigonal

Chemical Formula

SiO2 (with Fe2O3 inclusions)

Composition

Silicon dioxide with hematite (iron oxide) inclusions.

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