60ct 2.7" multi-colored green slice of liddicoatite tourmaline with triangles, from Madagascar
Liddicoatite (Ca(Li2Al) Al6( Si6O18)(BO3)3( OH)3F) is a calcium-rich lithium tourmaline, typically exhibiting extraordinarily beautiful geometrically patterned color zoning. It was recognized as a unique mineral species in 1977, and was named in honor of Richard T. Liddicoat, the “father of modern gemology. When it was first found, it was the sixth tourmaline species to be recognized; today 14 different tourmaline group members are recognized. Liddicoatite has physical and optical properties that are so similar to elbaite and rossmanite that analysis is required to distinguish the 3 species. To complicate matters further, 2 or even 3 may occur in a single crystal. The most famous historic source for these remarkable polychrome tourmalines was the Anjanabonoina pegmatite district in central Madagascar. Liddicoatite is only occasionally available today, most commonly seen as polished slices (cut perpendicular to the c-axis), which show off the characteristic zoning patterns.
GEOLOGIC ORIGINS
22ct 2.3" green, yellow and white slice of liddicoatite tourmaline with triangles, from Madagascar
Liddicoatite tourmaline crystals are found in gem-bearing cavities in granitic pegmatites. Their presence indicates that calcium was abundantly present during late-stage crystallization. The calcium may come one or more of three sources: from surrounding calcium-rich host rock; from alteration of calcium-bearing feldspars which had previously crystallized; or from conservation of calcium during earlier stages of pegmatite crystallization.
COLORS
28ct 2.4" Polished Slice Blue LIDDICOATITE TOURMALINE with triangles, from Madagascar
The most beautiful specimens are zoned varying shades of pink- to purplish-red, orange- pink to pinkish-orange, yellowish-green to bluish-green, brownish-green to brown to brownish-yellow, greenish-blue, blue, white, black, and colorless. These hues are present in a wide range of both tones (i.e., light to dark) and saturations (i.e., pale to intense), resulting in an almost infinite number of color variations.
PATTERNS AND COLOR ZONING
166ct 3.5" pink and red liddicoatite tourmaline slice with Mercedes Benz 3-ray star, from Russia
When slices are cut perpendicular to the c-axis, triangular zones and three-rayed “stars” resembling a Mercedes Benz symbol are Liddicoatite’s most recognizable features. Other characteristics include internal feature include strain patterns, partially healed fractures, feathers, needle-like tubes, negative crystals, and albite inclusions.
Slices with triangular zones around the core are especially sought-after. The multiple closely spaced color zones are defined by sharp to diffuse edges. Outer zones may be concentric, and are usually very narrow. Also, geochemical changes in the crystallization environment frequently produce both abrupt and gradual transitions from one color to another.
In other liddicoatite crystals, those three-ray star patterns, reminiscent of the Mercedes Benz symbol, are notable attributes of many Madagascar and Russian tourmaline. These stars are often pink or red, and cut through adjacent triangular zones before ending near the outer concentric color layers. One author (Zang, 1994) suggested that during crystallization under decreasing temperature, the red stars form as a result of the preferential incorporation of the large Mn2+ ion into the fast-growing pyramid {101–1} faces.
Three 26ct 1.3" slices from the same crystal of pink and red liddicoatite tourmaline with both star and triangle patterns, from Russia
