Iolite
Violet-blue "water sapphire" used by Viking navigators to locate the sun through clouds. India's Tamil Nadu alluvials, Sri Lanka and Tanzania's Usambara Mountains supply gem iolite with strong pleochroism.
Known origins & mines
Ratnapura Gem Fields · Sri Lanka
"City of Gems" — 2500 years of pit mining in river gravels yield ruby alongside nearly every other gem species. Sri Lankan ruby leans pink (…
Usambara Iolite Mines · Tanzania
The 1990s Usambara discovery yielded violet iolite crystals to 100 carats — Tanzanian material shows cleaner saturation than Indian alluvial…
Kodarma Tamil Nadu Iolite · India
Indian mica-belt diggings produce deep-violet iolite in quantity — the historic source for Jaipur's "water sapphire" trade since Mughal time…
Palmer Canyon Iolite · United States
Laramie Range deposit found in 1995 producing transparent blue iolite nodules up to thousands of carats, including the 1,714-ct Palmer Canyo…