Natural Tanzanite: Complete Guide for Trade, Jewelry, and Collections

This comprehensive guide provides everything you need to know about natural tanzanites, for trade partners, jewelers, and collectors alike.

Overview

Natural tanzanite, discovered in Tanzania in the 1960s, is a variety of zoisite known for its striking blue and violet colors. With a hardness of 6 to 7 on the Mohs scale, it offers moderate durability, making it suitable for various jewelry applications. Tanzanite's unique trichroism allows it to exhibit different colors when viewed from different angles, adding to its allure. As one of the most sought-after gemstones, understanding its characteristics, sourcing, and market trends is crucial for anyone involved in its trade or collection.

Physical Properties and Specifications

  • Chemical Composition: Ca₂Al₃(SiO₄)(Si₂O₇)O(OH)

  • Hardness: 6 - 7 on the Mohs scale

  • Crystal System: Orthorhombic

  • Refractive Index: 1.69 - 1.70

  • Specific Gravity: 3.35 - 3.40

  • Pleochroism: Strong, displaying blue, violet, and burgundy hues

  • Fluorescence: Weak fluorescence under UV light

  • Cleavage/Fracture: Perfect cleavage in two directions, conchoidal fracture

Color and Quality Classifications

Available Color Ranges

  • Primary hues: Blue, violet

  • Secondary modifications: Purplish-blue, bluish-purple

  • Tone and saturation ranges: Light to dark tones with vivid saturation

  • Premium colors: Deep blue with strong violet undertones

  • Commercial grades: Light blue to medium blue shades

Clarity Characteristics

  • Typical inclusion types: Needle-like inclusions, silk

  • Clarity grading standards: Eye-clean to included

  • Source-specific features: Unique inclusions that may indicate the origin

  1. Eye-clean criteria: No visible inclusions to the naked eye

Source Locations and Material

Historic sources

  • Tanzania (specifically the Merelani Hills)

Current production

  • The Merelani region remains the primary source of tanzanite.

Source-specific characteristics

  • Tanzanite from different mining sites can exhibit variations in color and clarity.

Production trends

  • Increasing demand coupled with limited supply has led to rising prices, making tanzanite more sought after.