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Quartz with Schorl Tourmaline is a mineral aggregate consisting of transparent to translucent quartz (silicon dioxide) with inclusions of black, prismatic crystals of schorl tourmaline. The schorl crystals can range from fine needles to thick, well-formed prisms, often appearing randomly oriented or in radiating patterns within the quartz. The contrast between the clear or milky quartz and the opaque black tourmaline creates a distinctive and aesthetically pleasing appearance.
How to Identify
- Color
- Quartz is typically colorless, white, or milky. Schorl tourmaline is opaque black.
- Luster
- Quartz has a vitreous (glassy) luster. Schorl tourmaline has a vitreous to resinous luster.
- Texture
- The texture is typically crystalline, with the quartz forming a massive or crystalline matrix and the schorl appearing as distinct, often elongated, prismatic crystals embedded within.
- Crystal Form
- Quartz often forms hexagonal prisms with pyramidal terminations, or massive anhedral grains. Schorl forms characteristic trigonal or hexagonal prisms, often with striations parallel to the c-axis, and can be acicular (needle-like), columnar, or massive.
- Cleavage
- Quartz has no true cleavage, exhibiting conchoidal fracture. Schorl tourmaline has very poor to indistinct cleavage parallel to the prism faces.
- Geological Environment
- Pegmatites, hydrothermal veins, granitic intrusions, and regionally metamorphosed rocks.
Key Facts
- Hardness: Quartz: 7 (Mohs); Schorl Tourmaline: 7-7.5 (Mohs)
- Specific Gravity: Quartz: 2.65; Schorl Tourmaline: 3.0-3.2
- Crystal System: Quartz: Trigonal; Schorl Tourmaline: Trigonal
- Color: Quartz: Colorless, white, milky; Schorl Tourmaline: Opaque black
- Luster: Vitreous
- Transparency: Quartz: Transparent to translucent; Schorl Tourmaline: Opaque
- Fracture: Quartz: Conchoidal; Schorl Tourmaline: Uneven to conchoidal
- Cleavage: Quartz: None; Schorl Tourmaline: Very poor to indistinct
- Composition: SiO2 (Quartz) and NaFe3Al6(BO3)3Si6O18(OH)4 (Schorl Tourmaline)
Quick Check
- Color: Colorless to milky white quartz with opaque black inclusions.
- Luster: Vitreous (glassy) for both components.
- Streak: White for quartz, colorless for schorl (though often not practical to obtain due to hardness).
Physical Characteristics
- Crystal Habit: Quartz: Prismatic, massive, granular; Schorl Tourmaline: Prismatic, acicular, columnar, massive, often with characteristic striations parallel to the c-axis.
- Cleavage Type: Quartz: None; Schorl Tourmaline: Very poor to indistinct on {1011} and {1120}.
- Fracture Type: Quartz: Conchoidal; Schorl Tourmaline: Uneven to conchoidal.
- Tenacity: Brittle for both minerals.
- Luster Type: Vitreous (glassy) for both.
Formation
This mineral aggregate forms primarily in pegmatites, hydrothermal veins, and some metamorphic rocks. Schorl, the iron-rich endmember of the tourmaline group, crystallizes from boron-rich, iron-rich fluids, often in association with quartz. As these fluids cool, schorl crystals grow within the quartz matrix or alongside quartz crystals. The formation can occur during the late stages of magmatic crystallization (pegmatitic stage) or during regional and contact metamorphism.
Usage
Primarily used as an ornamental stone, for lapidary purposes (cabochons, carvings), and in metaphysical practices. It is not typically used for industrial applications, as the individual minerals (quartz and schorl) have more specific industrial uses when separated.
Age Distribution
Found in geological formations ranging from Precambrian to Cenozoic, typically associated with granitic intrusions and metamorphic events.
Where to Find
Brazil
Minas Gerais is a prolific source, particularly for well-formed crystals in pegmatites.
United States
Maine (e.g., Mount Mica, Newry), California (e.g., Pala District), and Colorado are known for tourmaline-bearing pegmatites.
Pakistan
Northern areas, particularly Gilgit-Baltistan, produce fine specimens.
Afghanistan
Nuristan and Kunar provinces are known for pegmatite deposits.
Madagascar
Various localities yield tourmaline in quartz.
Finding Tips
Geological Context
Focus on areas known for pegmatites, granitic intrusions, or hydrothermal vein systems. Look for outcrops of these rock types.
Associated Minerals
Schorl tourmaline often co-occurs with feldspar, mica (muscovite, biotite), garnet, and other pegmatitic minerals. The presence of these can indicate a favorable environment.
Crystal Habit
Look for the characteristic prismatic, often striated, black crystals of schorl embedded in or growing alongside quartz. Schorl can sometimes form radiating aggregates.
Hardness Test
Quartz (Mohs 7) will scratch glass and steel. Schorl (Mohs 7-7.5) is slightly harder than quartz and will also scratch glass.
Density
Schorl is denser than quartz (SG 3.0-3.2 for schorl vs. 2.65 for quartz), so specimens with a high proportion of schorl may feel noticeably heavier than pure quartz of the same size.
Similar Rocks
Rutilated Quartz
SiO2 (Quartz) with TiO2 (Rutile)
Also known as: Hair of Venus
Actinolite in Quartz
SiO2 (Quartz) with Ca2(Mg,Fe)5Si8O22(OH)2 (Actinolite)
Also known as: Green Tourmalinated Quartz (misnomer)
Epidote in Quartz
SiO2 (Quartz) with Ca2(Al,Fe)3(SiO4)3(OH) (Epidote)
Also known as: Pistacite in Quartz
Scientific Classification
- Mineral Class
- Quartz: Tectosilicate; Schorl Tourmaline: Cyclosilicate
- Group
- Quartz Group; Tourmaline Group
- Crystal System
- Trigonal for both
- Chemical Formula
- SiO2 (Quartz) and NaFe3Al6(BO3)3Si6O18(OH)4 (Schorl Tourmaline)
- Composition
- Silicon dioxide (Quartz) and Sodium Iron Aluminum Borosilicate Hydroxide (Schorl Tourmaline)
Explore Schorl Tourmaline in Quartz
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