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Tourmalinated Quartz is a variety of quartz that contains acicular (needle-like) or prismatic inclusions of tourmaline. The quartz itself is typically clear, milky, or smoky, providing a transparent to translucent matrix for the tourmaline. The tourmaline inclusions are most commonly black schorl, but can also be other varieties like green or pink elbaite, though these are rarer. The tourmaline crystals are often randomly oriented, but can sometimes show parallel alignment within the quartz. The aesthetic contrast between the host quartz and the included tourmaline makes it a distinctive and sought-after mineral specimen.
How to Identify
- Color
- Quartz matrix can be colorless, white, smoky, or rarely other hues. Tourmaline inclusions are typically black (schorl), but can be dark green, brown, or rarely other colors.
- Luster
- Vitreous (glassy) for both quartz and tourmaline.
- Texture
- Crystalline, with distinct acicular or prismatic tourmaline crystals embedded within a larger quartz crystal.
- Crystal Form
- Quartz typically forms hexagonal prisms with pyramidal terminations. Tourmaline forms trigonal prisms, often with striations parallel to the c-axis, embedded within the quartz.
- Cleavage
- Quartz: None. Tourmaline: Poor basal cleavage, often not observable in inclusions.
- Geological Environment
- Granitic pegmatites, hydrothermal veins, and some metamorphic rocks.
Key Facts
- Hardness: Quartz: 7 on Mohs scale. Tourmaline: 7-7.5 on Mohs scale.
- Specific Gravity: Quartz: 2.65 g/cm³. Tourmaline: 3.0-3.26 g/cm³ (varies with composition).
- Crystal System: Quartz: Trigonal. Tourmaline: Trigonal.
- Color: Colorless, white, or smoky quartz with black, dark green, or brown tourmaline inclusions.
- Luster: Vitreous.
- Transparency: Transparent to translucent (quartz), opaque to translucent (tourmaline inclusions).
- Fracture: Conchoidal (quartz), uneven to conchoidal (tourmaline).
- Cleavage: Quartz: None. Tourmaline: Poor basal cleavage, often not observed.
- Composition: SiO2 (Quartz) with complex borosilicate (Tourmaline Group).
Quick Check
- Color: Clear to smoky quartz with black needle-like inclusions.
- Luster: Vitreous.
- Streak: White (for quartz), colorless (for tourmaline, though typically not tested on inclusions).
Physical Characteristics
- Crystal Habit: Quartz typically forms prismatic crystals with hexagonal cross-sections and pyramidal terminations. Tourmaline inclusions are acicular to prismatic, often with characteristic triangular cross-sections and vertical striations.
- Cleavage Type: Quartz: Absent. Tourmaline: Imperfect to poor on {1011} and {0001}.
- Fracture Type: Conchoidal in quartz, uneven to conchoidal in tourmaline.
- Tenacity: Brittle for both minerals.
- Luster Type: Vitreous (glassy).
Formation
Tourmalinated Quartz forms primarily in pegmatites, granites, and high-temperature hydrothermal veins. Quartz crystallizes from silica-rich fluids, and tourmaline (often schorl, the iron-rich variety, or elbaite) crystallizes simultaneously or subsequently within the same geological environment. The tourmaline crystals become encapsulated within the growing quartz crystal, forming needle-like or prismatic inclusions. This often occurs during the late stages of magmatic differentiation or during regional metamorphism.
Usage
Primarily used as an ornamental stone, for lapidary purposes (cabochons, spheres, carvings), and in jewelry. It is also a popular specimen for mineral collectors due to its aesthetic appeal. It has no significant industrial uses beyond its constituent minerals.
Age Distribution
Found in geological formations ranging from Precambrian to Cenozoic, wherever pegmatites, granites, and metamorphic rocks occur.
Where to Find
Brazil
Minas Gerais is a prolific source, particularly for high-quality specimens with clear quartz and well-formed black tourmaline needles.
United States
Localities in Maine (e.g., Mount Mica, Dunton Quarry) and California (e.g., Pala District) are known for tourmaline-bearing pegmatites, sometimes yielding tourmalinated quartz.
Pakistan
Northern areas, particularly Gilgit-Baltistan, produce fine specimens of quartz with various tourmaline inclusions.
Madagascar
Known for a wide variety of quartz and tourmaline, including specimens where tourmaline is included in quartz.
Afghanistan
Similar to Pakistan, pegmatite regions yield quartz with tourmaline inclusions.
Finding Tips
Look in Pegmatites
Focus your search on granitic pegmatite dikes, as these are the primary environments for the formation of large, well-formed quartz and tourmaline crystals.
Hydrothermal Veins
Explore quartz veins associated with granitic intrusions, as hydrothermal activity can lead to the co-crystallization of quartz and tourmaline.
Examine Quartz Closely
When collecting quartz, especially clear or smoky varieties, carefully inspect for internal inclusions. Tourmaline needles can be very fine.
Check Mine Dumps
Old mine dumps from pegmatite or granite quarries can be excellent places to find discarded but still valuable specimens.
Similar Rocks
Rutilated Quartz
SiO2 (Quartz) with TiO2 (Rutile)
Also known as: Quartz with Rutile
Actinolite in Quartz
SiO2 (Quartz) with Ca2(Mg,Fe)5Si8O22(OH)2 (Actinolite)
Also known as: Amphibole Quartz
Epidote in Quartz
SiO2 (Quartz) with Ca2(Al,Fe)3(SiO4)3(OH) (Epidote)
Also known as: Epidote Quartz
Scientific Classification
- Mineral Class
- Silicate (Quartz), Cyclosilicate (Tourmaline Group)
- Group
- Quartz Group, Tourmaline Group
- Crystal System
- Trigonal (both Quartz and Tourmaline)
- Chemical Formula
- SiO2 (Quartz) with (Na,Ca)(Li,Mg,Fe,Mn,Al)3Al6(BO3)3Si6O18(OH)4 (Tourmaline Group)
- Composition
- Silicon dioxide (Quartz) with a complex borosilicate (Tourmaline), varying significantly based on the specific tourmaline species present (e.g., schorl, elbaite, dravite).
Explore Tourmalinated Quartz
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