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Microcline with Schorl refers to the common mineral association where black, prismatic crystals of Schorl (a variety of tourmaline) are found embedded within or growing alongside Microcline, a potassium feldspar. This association is characteristic of granitic pegmatites. Microcline typically forms large, blocky crystals, often exhibiting a pale pink, white, or green (amazonite) color, while Schorl appears as distinct, often striated, black crystals.
How to Identify
- Color
- Microcline: White, cream, pale yellow, pink, reddish, or green (amazonite). Schorl: Opaque black.
- Luster
- Microcline: Vitreous to pearly. Schorl: Vitreous to resinous.
- Texture
- Coarse-grained, with distinct crystals of both minerals visible. Microcline often shows perthitic exsolution lamellae. Schorl crystals are typically prismatic.
- Crystal Form
- Microcline: Triclinic, typically forming blocky, anhedral to subhedral crystals, often twinned (e.g., Carlsbad, Baveno, Manebach). Schorl: Hexagonal (trigonal), forming elongated, prismatic crystals with characteristic vertical striations on prism faces and a pseudo-triangular cross-section.
- Cleavage
- Microcline: Two distinct cleavages at nearly 90 degrees (89°30'). Schorl: Indistinct to poor cleavage, typically exhibiting conchoidal to uneven fracture.
- Geological Environment
- Primarily granitic pegmatites, but also in some granites, aplites, and metamorphic rocks.
Key Facts
- Hardness: Microcline: 6-6.5 (Mohs); Schorl: 7-7.5 (Mohs)
- Specific Gravity: Microcline: 2.54-2.57; Schorl: 3.03-3.25
- Crystal System: Microcline: Triclinic; Schorl: Trigonal (Hexagonal)
- Color: Microcline: White, cream, pink, green; Schorl: Opaque black
- Luster: Microcline: Vitreous to pearly; Schorl: Vitreous to resinous
- Transparency: Microcline: Translucent to opaque; Schorl: Opaque
- Fracture: Microcline: Uneven to conchoidal; Schorl: Conchoidal to uneven
- Cleavage: Microcline: Perfect in two directions at nearly 90 degrees; Schorl: Indistinct to poor
- Composition: Microcline: Potassium aluminum silicate; Schorl: Sodium iron aluminum borosilicate hydroxide
Quick Check
- Color: Microcline: White, pink, green; Schorl: Opaque black
- Luster: Vitreous to pearly (Microcline), Vitreous to resinous (Schorl)
- Streak: White (Microcline), White to colorless (Schorl)
Physical Characteristics
- Crystal Habit: Microcline: Blocky, tabular, often twinned; Schorl: Prismatic, columnar, acicular, often striated vertically
- Cleavage Type: Microcline: Perfect {001} and {010} at 89°30'; Schorl: Indistinct {1011} and {0001}
- Fracture Type: Microcline: Uneven to conchoidal; Schorl: Conchoidal to uneven
- Tenacity: Microcline: Brittle; Schorl: Brittle
- Luster Type: Microcline: Vitreous to pearly; Schorl: Vitreous to resinous
Formation
Microcline and Schorl commonly form together in granitic pegmatites, which are coarse-grained igneous rocks formed from the slow crystallization of magma rich in volatile components (like water, boron, and fluorine) during the final stages of magmatic differentiation. Schorl crystallizes from boron-rich fluids, often in association with potassium feldspars like microcline, quartz, and micas.
Usage
Microcline is used in ceramics, glass manufacturing, and as an abrasive. Schorl, while not typically used industrially due to its commonality and opaque nature, is a popular mineral for collectors and is sometimes used in ornamental carvings or as a minor gemstone. The combination is primarily of interest to mineral collectors and geologists.
Age Distribution
Found in various geological ages, primarily associated with granitic pegmatites which can range from Precambrian to Cenozoic.
Where to Find
Brazil
Minas Gerais is famous for large pegmatite deposits yielding excellent specimens of both microcline (including amazonite) and schorl.
United States
Maine, California (Pala District), Colorado (Pikes Peak region for amazonite), and North Carolina have significant pegmatite occurrences with microcline and schorl.
Madagascar
Known for various pegmatite minerals, including large microcline crystals and schorl.
Russia
The Ural Mountains and Kola Peninsula are sources of microcline and schorl, particularly amazonite.
Pakistan
Northern areas are known for pegmatite minerals, including schorl and microcline.
Finding Tips
Target Pegmatites
Focus your search on granitic pegmatite outcrops, which are the primary geological environment for this association. Look for coarse-grained igneous rocks.
Look for Crystal Forms
Identify the blocky, often twinned crystals of microcline and the distinct, elongated, striated black prisms of schorl.
Check for Color and Luster
Microcline's characteristic colors (pink, white, green) and vitreous luster, combined with schorl's opaque black color and vitreous luster, are good indicators.
Examine Cleavage and Fracture
Microcline's two cleavages at nearly 90 degrees are diagnostic. Schorl's lack of good cleavage and conchoidal fracture can help differentiate it from other black minerals.
Similar Rocks
Orthoclase with Tourmaline
KAlSi3O8 (Orthoclase) and NaFe3Al6(BO3)3Si6O18(OH)4 (Schorl)
Also known as: Black Tourmaline in Feldspar
Albite with Tourmaline
NaAlSi3O8 (Albite) and NaFe3Al6(BO3)3Si6O18(OH)4 (Schorl)
Also known as: Black Tourmaline in Feldspar
Quartz with Tourmaline
SiO2 (Quartz) and NaFe3Al6(BO3)3Si6O18(OH)4 (Schorl)
Also known as: Tourmalinated Quartz
Scientific Classification
- Mineral Class
- Microcline: Tectosilicate (Feldspar Group); Schorl: Cyclosilicate (Tourmaline Group)
- Group
- Microcline: Feldspar Group; Schorl: Tourmaline Group
- Crystal System
- Microcline: Triclinic; Schorl: Trigonal
- Chemical Formula
- Microcline: KAlSi3O8; Schorl: NaFe3Al6(BO3)3Si6O18(OH)4
- Composition
- Microcline: Potassium, aluminum, silicon, oxygen; Schorl: Sodium, iron, aluminum, boron, silicon, oxygen, hydrogen
Explore Microcline with Schorl
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