18.10 carats bicoloUr tourmaline crystals form Afghanistan untreated and uheated Chemical Composition: Complex boron silicate with aluminum, iron, magnesium, lithium, sodium, and other elements. • Crystal System: Trigonal. • Hardness: 7–7.5 on the Mohs scale, making it suitable for everyday jewelry. • Color: Found in almost every color, including black, green, blue, pink, red, yellow, brown, and multicolored varieties. • Luster: Vitreous (glassy). • Transparency: Transparent to opaque, with transparent stones being the most valuable. • Refractive Index: Approximately 1.61–1.66. • Specific Gravity: About 3.00–3.26, depending on composition. • Cleavage: Indistinct to poor. • Fracture: Uneven to conchoidal. • Pleochroism: Strong, showing different colors or color intensities from different viewing directions. • Inclusions: May contain liquid-filled tubes, growth lines, and natural mineral inclusions that help identify natural stones. • Special Properties: Exhibits pyroelectricity and piezoelectricity, meaning it can develop an electric charge when heated or under pressure. • Durability: Good toughness and resistance to wear, making it ideal for rings, pendants, earrings, and other jewelry. • Major Sources: Brazil, Afghanistan, Pakistan, Mozambique, Nigeria, Madagascar, Sri Lanka, Namibia, and the United States.