Bi-Color Tourmaline (or Watermelon Tourmaline)

Hardness: 7-7.5 (Mohs scale); Color: Pink to red and green (bi-color, often with a clear boundary, resembling a watermelon slice when cut); Luster: Vitreous to resinous; Crystal structure: Hexagonal (trigonal); Cleavage: Indistinct; Specific Gravity: 3.0-3.26.

Tourmaline forms in igneous and metamorphic rocks. Specifically, bi-color tourmaline often crystallizes in granitic pegmatites, which are coarse-grained igneous rocks that form from the last stages of magma crystallization. The different color zones are a result of changes in the chemical composition of the fluid during crystal growth, particularly variations in trace elements like manganese (for pink/red) and iron or chromium (for green). Geological age varies, often found in ancient and geologically stable regions.

Predominantly used as a gemstone in jewelry due to its striking colors and durability. Well-formed crystals are highly prized by mineral collectors. It is sometimes used in pressure gauges due to its pyroelectric and piezoelectric properties (though less common for bi-color varieties).

Tourmaline is not a single mineral but a group of closely related mineral species. Bi-color tourmaline, especially "Watermelon Tourmaline," is highly sought after. It is believed to promote inspiration, reduce fear, and build self-confidence. Ancient legend says tourmaline was formed from a rainbow as it traveled from the Earth to the sun, which explains its many vibrant colors. Color zoning can be quite intricate, showing multiple bands of color within a single crystal.

In the field, look for well-formed hexagonal crystals in pegmatite veins or alluvial deposits. Its hardness and characteristic vitreous luster are key identifiers. Often found in Brazil (Minas Gerais), Afghanistan, Pakistan, Africa (e.g., Nigeria, Mozambique), and the USA (e.g., Maine, California). Identification tips include observing its distinct bi-colors, often with a sharp line between colors, and its characteristic triangular cross-section in natural crystal forms. Testing for hardness can also distinguish it from softer minerals.