Limonite/Goethite Crust on Quartz
Goethite (Iron Oxyhydroxide) over Quartz (Silicon Dioxide) · Mineral Specimen / Decorative Stone
Crystal System
Orthorhombic (Goethite) and Trigonal (Quartz support); appears as botryoidal, micro-crystalline druzy, or earthy crusts
Mineral Group
Oxides / Hydroxides (Goethite) and Silicates (Quartz support)
Chemical Formula
α-Fe3+O(OH) over SiO2 with trace Fe2O3
Formation Process
Secondary formation via the weathering (oxidation) of iron-rich minerals in hydrothermal veins or sedimentary environments; low-temperature aqueous precipitation.
About This Crystal
The specimen features a thick, porous, and earthy iron oxide crust (Limonite/Goethite) with a warm brownish-orange to ochre color. Tiny micro-crystalline druzy points create a sparkling 'glitter' effect across the irregular surface. The texture is rough and cavernous.
Physical Characteristics
Color: Brownish-orange, yellowish-brown; Streak: Yellowish-brown; Cleavage: Perfect on {010} (microscopic); Fracture: Uneven to splintery; Luster: Dull to sub-vitreous sparkling; Density: 3.3-4.3 (Goethite); Fluorescence: Usually none.
Optical Properties
Sub-adamantine to dull luster; the micro-crystals exhibit high reflectivity (specular flashes) despite the overall opaque body of the crust. Refractive index is high (2.26-2.39) but difficult to measure in this form.
Hardness & Durability
Origin Region
Common in oxidation zones; notable sources include Morocco, Brazil, and the United States (Colorado, Arizona). Often found in gossans and weathered iron deposits.
Hardness & Durability
Mohs hardness 5.0 - 5.5 for the Goethite crust; underlying Quartz is 7.0. The crust is brittle and can be prone to crumbling or staining if handled roughly.
Care & Maintenance
Avoid acidic cleaners which may dissolve the iron oxide. Clean only with soft brush or dry air. Avoid prolonged submersion in water; do not use ultrasonic cleaners. Store away from humidity to prevent further oxidation or crumbling.
Rarity & Value
Common mineral; value is primarily aesthetic based on the 'sparkle' and form. Generally inexpensive ($5-$50 for hand specimens) unless paired with rare secondary minerals.
Special Characteristics
Displays 'druzy' sparkle from microscopic crystal faces; the cavernous 'vuggy' structure is typical of weathered gossan material.
Lore & History
Historically, limonite and goethite were used as ochre pigments for cave paintings and pottery. In metaphysical traditions, it is associated with grounding, stamina, and the Root Chakra, believed to help one remain stable during periods of change.