Tsilaisite
Na(Mn2+3)Al6(Si6O18)(BO3)3(OH)3(OH)
A manganese-dominant tourmaline, the source of bright yellow to greenish-yellow gem tourmaline, named for its Madagascar type locality.
- Mohs hardness
- 7-7.5
- Color
- Yellow to greenish-yellow
- Type
- mineral
Got a rock like this?
Identify any rock from a photo, free.
Overview
Tsilaisite is the manganese-dominant end-member of the tourmaline supergroup, the manganese analogue of elbaite. Manganese in its octahedral sites produces a distinctive bright yellow to greenish-yellow color, the same chemistry behind many "canary" yellow gem tourmalines.
Long used informally as a name for manganoan elbaite, tsilaisite was formally approved as a valid species in 2013 once material with true manganese dominance was characterized. It is named for the Tsilaisina locality in Madagascar.
It is one of the more gem-relevant of the rarer tourmaline species, since manganese-rich crystals can be transparent and vividly colored.
Formation & geology
Tsilaisite forms in lithium- and manganese-enriched granitic pegmatites, the highly evolved magmatic-hydrothermal systems that also yield elbaite. Manganese concentrated in residual pegmatite fluids enters the tourmaline structure in place of the iron, magnesium, or lithium of other species.
Its type locality is Tsilaisina (Tsilaizina), Madagascar, a region famous for colorful tourmalines. Manganese-bearing yellow tourmalines also come from places like Zambia, Malawi, and Nigeria.
The pocket zones of these pegmatites, where rare elements concentrate, are the prime setting for manganese-dominant tourmaline.
How to identify it
Tsilaisite and manganese-rich tourmalines show bright yellow to greenish-yellow color, vitreous luster, hardness 7-7.5, strong pleochroism, and the striated prismatic habit and triangular cross-section of tourmaline. There is no cleavage.
Visual identification of true tsilaisite versus manganoan elbaite is impossible without chemistry confirming manganese dominance. Within the yellow gem trade, the color alone is the practical clue.
Look-alikes include yellow beryl (heliodor), citrine, and yellow sapphire; tourmaline's pleochroism, striations, and refractive index help separate them.
Uses & significance
Manganese-rich tourmaline of tsilaisite composition is cut into attractive canary and greenish-yellow gemstones prized for their vivid, slightly neon color. Clean, well-colored stones command solid prices among colored-gem collectors.
As a defined mineral species, tsilaisite is also collected as crystal specimens and studied for tourmaline chemistry. Metaphysically, yellow tourmalines are associated with the solar plexus, confidence, and energy, though that use is not scientific.
Frequently asked questions
What gives tsilaisite its yellow color?
Manganese in the tourmaline structure produces its bright yellow to greenish-yellow hue.
Is tsilaisite the same as yellow elbaite?
They are closely related; tsilaisite is the manganese-dominant species, while many yellow gem tourmalines are manganese-bearing elbaite.
Where does tsilaisite come from?
Its type locality is Tsilaisina, Madagascar, and manganese-rich yellow tourmalines also come from Zambia, Malawi, and Nigeria.
Can tsilaisite be a gemstone?
Yes; transparent manganese-rich crystals are faceted into vivid yellow gems valued by collectors.
Tsilaisite guides
In-depth guides for identifying, valuing, and understanding Tsilaisite.
