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Quartz with Tourmaline is a mineral aggregate consisting of transparent to translucent quartz (silicon dioxide) with acicular (needle-like) or prismatic crystals of tourmaline embedded within it. The tourmaline inclusions are most commonly black (schorl), but can also be other colors depending on the tourmaline species present. The quartz matrix can be clear, milky, or smoky. The contrast between the clear quartz and the dark tourmaline needles creates a distinctive and attractive appearance.
How to Identify
- Color
- Clear, milky, or smoky quartz with black (most common), dark green, or rarely other colored needle-like or prismatic tourmaline inclusions.
- Luster
- Vitreous (glassy) for both quartz and tourmaline.
- Texture
- Smooth to conchoidal fracture surfaces for quartz; tourmaline inclusions are typically smooth and prismatic.
- Crystal Form
- Quartz typically forms hexagonal prisms with pyramidal terminations; tourmaline forms elongated prismatic crystals, often with characteristic triangular cross-sections, embedded within the quartz.
- Cleavage
- Quartz has no true cleavage, exhibiting conchoidal fracture. Tourmaline has poor to indistinct cleavage, often appearing as brittle fracture.
- Geological Environment
- Granitic pegmatites, hydrothermal veins, and granitic intrusions. It is often found in association with other pegmatitic minerals.
Key Facts
- Hardness: Quartz: 7 on Mohs scale. Tourmaline: 7-7.5 on Mohs scale. The aggregate will generally be around 7.
- Specific Gravity: Quartz: 2.65 g/cm³. Tourmaline: 3.0-3.26 g/cm³. The aggregate will be slightly higher than pure quartz, typically around 2.65-2.75 g/cm³.
- Crystal System: Quartz: Trigonal. Tourmaline: Trigonal.
- Color: Colorless, white, or smoky quartz with black, dark green, or rarely other colored tourmaline inclusions.
- Luster: Vitreous.
- Transparency: Transparent to translucent.
- Fracture: Conchoidal (quartz); uneven to conchoidal (tourmaline).
- Cleavage: None (quartz); poor to indistinct (tourmaline).
- Composition: Silicon dioxide (SiO2) for quartz, and a complex borosilicate for tourmaline, with general formula XY3Z6(T6O18)(BO3)3V3W, where X, Y, Z, T, V, W represent various cations and anions.
Quick Check
- Color: Clear, milky, or smoky quartz with black needle-like inclusions.
- Luster: Vitreous (glassy).
- Streak: White (for quartz); colorless (for tourmaline, though often not practical to streak inclusions).
Physical Characteristics
- Crystal Habit: Quartz typically forms prismatic crystals; tourmaline forms acicular to prismatic crystals embedded within the quartz.
- Cleavage Type: Quartz: None. Tourmaline: Poor to indistinct on {1011} and {0001}.
- Fracture Type: Conchoidal (quartz); uneven to conchoidal (tourmaline).
- Tenacity: Brittle.
- Luster Type: Vitreous.
Formation
Tourmalinated Quartz forms when tourmaline crystals grow within a quartz matrix. This typically occurs in hydrothermal veins, pegmatites, and granitic rocks where both silicon dioxide and the complex borosilicate components for tourmaline are present. The tourmaline often crystallizes first, or simultaneously, within the growing quartz crystals, leading to inclusions. The formation temperature and pressure conditions are characteristic of magmatic and hydrothermal environments, generally between 200°C and 700°C and moderate to high pressures.
Usage
Primarily used as an ornamental stone, for lapidary purposes, and in jewelry. Due to its aesthetic appeal, it is popular for carvings, cabochons, beads, and polished specimens. It also holds significance in metaphysical and healing practices.
Age Distribution
Found in geological formations ranging from Precambrian to Cenozoic, typically associated with granitic intrusions and pegmatites.
Where to Find
Brazil
Minas Gerais is a significant source, particularly for high-quality specimens used in jewelry.
United States
Localities in Maine, California (e.g., Pala, Mesa Grande), and Colorado are known for tourmaline-bearing pegmatites.
Madagascar
Produces various forms of tourmaline and quartz, including tourmalinated quartz.
Pakistan
Northern areas are known for pegmatite deposits yielding fine mineral specimens.
Afghanistan
Similar to Pakistan, pegmatite regions yield good quality tourmalinated quartz.
Finding Tips
Look in Pegmatites
Focus your search on granitic pegmatite dikes, which are coarse-grained igneous rocks known for hosting large, well-formed crystals of quartz and various tourmaline species.
Hydrothermal Veins
Explore quartz veins that cut through granitic or metamorphic rocks, as these can be sites of hydrothermal mineralization where tourmaline and quartz co-crystallize.
Examine Rock Dumps
Old mine dumps, especially those from gem or feldspar mines, can be excellent places to find discarded but valuable specimens.
Identify Tourmaline Habit
Learn to recognize the characteristic prismatic, often striated, habit of tourmaline crystals, even when embedded in quartz. Black tourmaline (schorl) is the most common inclusion.
Check for Transparency
High-quality specimens will have clear, transparent quartz, allowing the tourmaline inclusions to be seen distinctly. Milky or smoky quartz can also host tourmaline.
Similar Rocks
Rutilated Quartz
Quartz (SiO2) with Rutile (TiO2)
Also known as: Quartz with Rutile
Actinolite in Quartz
Quartz (SiO2) with Actinolite (Ca2(Mg,Fe)5Si8O22(OH)2)
Also known as: Actinolite Quartz
Epidote in Quartz
Quartz (SiO2) with Epidote (Ca2(Al,Fe)3(SiO4)3(OH))
Also known as: Epidote Quartz
Scientific Classification
- Mineral Class
- Silicate (Quartz: Tectosilicate; Tourmaline: Cyclosilicate)
- Group
- Quartz Group (for Quartz); Tourmaline Group (for Tourmaline)
- Crystal System
- Trigonal
- Chemical Formula
- SiO2 (Quartz) + (Na,Ca)(Li,Mg,Fe,Al)3Al6(BO3)3Si6O18(OH)4 (General Tourmaline Formula)
- Composition
- Silicon dioxide with complex borosilicates of aluminum, iron, magnesium, sodium, lithium, and other elements.
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