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Cobalt spinel is a rare gemstone primarily known for its vivid, deep blue color, which gets its intensity from the presence of cobalt. It is a form of magnesium aluminate, with a high refractive index, vitreous luster, and a durability of 7.5 to 8 on the Mohs hardness scale, making it suitable for jewelry. While valued for its striking appearance, it is distinct from other blue spinels because cobalt is the dominant coloring agent, not iron, which can cause grayish or greenish tints.

Key characteristics

Color: A vibrant, saturated cobalt blue that can rival the finest sapphires. The color can range from a rich blue to lighter shades with violet undertones.

Composition: Primarily magnesium aluminate, with cobalt as the key coloring agent.

Hardness: 7.5 to 8 on the Mohs scale, making it a durable gemstone for jewelry.

Luster: Vitreous, or glass-like.

Transparency: Typically transparent with a glass-like appearance.

Origins: Notable deposits are found in locations like Sri Lanka, Myanmar, Tanzania, and Vietnam.

Identification

Color: The most distinctive feature is its intense blue color.

Microscopic features: Macroscopic features like "healed fractures" and "fingerprint" patterns, as well as various mineral inclusions like olivine and pargasite, can help with identification.

Fluorescence: May fluoresce pink or red under UV light due to the presence of cobalt.

Magnetism: Some natural cobalt spinels may exhibit magnetic properties due to the presence of iron.

Value

Rarity: Gem-quality, vivid cobalt spinels are rare and can be more expensive than other blue spinels.

Color: The intensity and purity of the blue color directly influence its value.

Metaphysical properties

In metaphysical beliefs, it is associated with clarity of thought, communication, creativity, and tranquility.