Calcareous Tufa (Travertine)
Calcite (variety: Tufa) · Mineral Specimen / Sedimentary Rock Component
Crystal System
Trigonal; typically occurs in massive, porous, or microcrystalline habits
Mineral Group
Carbonates (Calcite Group)
Chemical Formula
CaCO3
Formation Process
Sedimentary; formed by the rapid chemical precipitation of calcium carbonate from ambient-temperature water, often around springs, lake shores, or areas with high calcium concentrations.
About This Crystal
A porous, cream-to-white colored specimen with a dull, earthy luster. The surface is irregular and pitted, showing a microcrystalline structure without large visible crystal faces. It appears opaque with a chalky texture.
Physical Characteristics
Color: White to light grey; Streak: White; Cleavage: Perfect rhombohedral (though rarely visible in tufa form); Fracture: Uneven; Specific Gravity: Approx 2.7; Fluorescence: May show weak yellow or white fluorescence under UV; Effervesces vigorously with dilute hydrochloric acid.
Optical Properties
Refractive Index: 1.486-1.658; Birefringence: 0.172 (very high, but masked by microcrystalline nature); Pleochroism: None; Uniaxial negative.
Hardness & Durability
Origin Region
Found worldwide in areas with limestone bedrock; notably the Mammoth Hot Springs (USA), Pamukkale (Turkey), and various karst regions in Europe.
Hardness & Durability
Mohs Hardness: 3.0; Toughness: Poor; very brittle and prone to scratching or crumbling due to high porosity.
Care & Maintenance
Clean with dry soft brush only; avoid all acids (including vinegar) and ultrasonic cleaners. Store in a dry environment and handle gently to prevent breakage.
Rarity & Value
Common; generally low value as a mineral specimen. Most valuable in large decorative slabs or when featuring unique organic impressions.
Special Characteristics
Extreme porosity; ability to capture impressions of plants or mosses (biological inclusions); rapid effervescence in acid.
Lore & History
Historically used as a lightweight building material in ancient Rome and Europe. Culturally associated with grounding and stability in traditional lore; often linked to the Root Chakra.