London Blue Topaz

London blue topaz is a trade-color grade of blue topaz, the deepest and most saturated of the three common blue tones (Sky, Swiss, and London). It shows a rich, slightly inky steel-blue, sometimes with greenish or grey undertones, that distinguishes it from the brighter Swiss blue and the pale Sky blue.

Like nearly all blue topaz, its color is produced by treating colorless natural topaz with irradiation followed by heating. London blue typically results from specific irradiation processes that yield the darkest stable tone.

With a hardness of 8 and excellent transparency, it is one of the most popular affordable blue gemstones in modern jewelry.

The host mineral, topaz, forms in fluorine-rich late-stage igneous environments, especially granitic pegmatites and rhyolite cavities, as well as high-temperature hydrothermal veins. Durable crystals also accumulate in alluvial gem gravels.

The London blue color itself is not natural in this depth. Colorless topaz is exposed to irradiation, which creates color centers, and then gently heated to stabilize the deep blue. The treatment is permanent and standard throughout the industry.

Brazil and Nigeria are leading sources of the colorless topaz used, with treatment performed in specialized facilities. The finished stones are color-stable under normal wear.

Look for a transparent stone in deep, slightly greyed or greenish steel-blue, darker and more muted than Swiss blue topaz. Hardness is 8, with perfect basal cleavage and a vitreous luster; streak is white.

Topaz's relatively high specific gravity (about 3.5) makes it feel heavy for its size compared with blue quartz or glass. It is markedly harder than blue chalcedony or apatite look-alikes.

Distinguish it from blue zircon (higher dispersion and birefringence, often visible facet doubling) and from synthetic spinel or glass imitations via hardness, density, and refractometer readings. The cleavage separates it from quartz.

London blue topaz is used almost exclusively in jewelry. Its deep color and large available sizes make it a favorite for rings, pendants, and earrings, often set in white or yellow gold and sterling silver.

Its affordability relative to sapphire, combined with good hardness, makes it a practical everyday blue gemstone, though its perfect cleavage warrants protective settings for rings.

Metaphysically, blue topaz is linked to communication, calm, and the throat chakra, said to promote clear expression and tranquility. These associations are spiritual beliefs and not scientifically established.