Pegmatite Matrix with Black Tourmaline and Feldspar
Granite Pegmatite containing Quartz, Feldspar, and Tourmaline (Schorl) · Mineral Specimen
Crystal System
Triclinic and Monoclinic (Feldspar), Trigonal (Quartz and Tourmaline)
Mineral Group
Silicates (Tectosilicates and Cyclosilicates)
Chemical Formula
Complex silicate mineral assemblage containing SiO2 (Quartz), NaAlSi3O8/KAlSi3O8 (Feldspar), and NaFe2+3Al6(Si6O18)(BO33)(OH)4 (Schorl Tourmaline)
Formation Process
Igneous pegmatitic process involving the slow cooling of volatile-rich magma deep within the Earth's crust, allowing large crystals to form
About This Crystal
This specimen is a coarse-grained pegmatite rock matrix exhibiting a mix of light-colored feldspar and quartz minerals with brownish-yellow iron-stained areas, complemented by a notable dark, black tourmaline (schorl) aggregate embedded in the upper left corner. The luster varies from vitreous on clear crystal faces to pearly or dull on cleavage planes of the feldspar.
Physical Characteristics
Color ranges from white, cream, and tan to deep brownish-yellow due to iron oxide staining, with a contrasting black patch of tourmaline. Streak is white for the felsic minerals and greyish-black for schorl. Hardness typically averages 6 to 7 on the Mohs scale for the overall matrix. Cleavage is good in two directions for the feldspar components, and fracture is uneven to conchoidal.
Optical Properties
Felsic minerals are translucent to opaque with standard double or single refraction depending on the specific constituent. Non-pleochroic in mass, but constituent quartz and feldspar show standard optical signatures under polarized light.
Hardness & Durability
Origin Region
Common worldwide in pegmatite-rich areas such as Minas Gerais (Brazil), Madagascar, and various regions in the United States
Hardness & Durability
Mohs hardness of approximately 6 to 7. The specimen is relatively durable as a raw mineral rock, though individual feldspar cleavage planes can be sensitive to sharp impacts.
Care & Maintenance
Clean with warm soapy water and a soft brush. Avoid harsh chemical cleaners and extended exposure to strong acids. Store safely away from softer stones that might scratch.
Rarity & Value
Common as a geological specimen. Value depends primarily on the aesthetic contrast, size, and perfection of accessory crystals like tourmaline or beryl embedded within the matrix.
Special Characteristics
Features a striking color contrast between the light-colored, iron-stained feldspathic matrix and the dark, prismatic-textured black schorl tourmaline inclusion.
Lore & History
Pegmatites are often viewed in metaphysical practices as stones of balancing energies, integrating the grounding protective properties of black tourmaline with the amplifying and clarifying qualities of quartz and feldspar.