Iolite vs Tanzanite: What’s the Difference Between These Stunning Gemstones?

When it comes to choosing between iolite and tanzanite, many jewellery enthusiasts find themselves puzzled.

In short: Iolite (cordierite, Mohs 7-7.5) shows violet-blue with strong pleochroism; tanzanite (zoisite, Mohs 6.5-7) shows similar colours but more saturated. Iolite costs roughly 5-10% of equivalent tanzanite per carat — making it the affordable lookalike. Tanzanite is rarer, found only at one mine in Tanzania; iolite is widely sourced from India, Sri Lanka and Brazil.

Both gemstones exhibit captivating blue and violet hues, making them popular choices for various adornments.

However, despite their visual similarities, iolite and tanzanite differ significantly in origin, composition, durability, and value.

Let's look at these distinctions to help you make an informed decision.

Origins and Discovery

Iolite has a rich history dating back centuries.

Historically, Viking navigators are believed to have used thin slices of iolite as polarising filters to locate the sun on overcast days, aiding their voyages across the Atlantic.

Today, iolite is primarily sourced from countries such as India, Sri Lanka, Brazil, and Madagascar.

Tanzanite, in contrast, is a relatively recent discovery.

Unearthed in the 1960s, this gemstone is found exclusively in the Merelani Hills near Mount Kilimanjaro in Tanzania.

Its limited geographic source contributes to its rarity and allure.

Colour Variations and Pleochroism

A striking feature of both gemstones is their pleochroism—the ability to display different colours when viewed from various angles.