Cobalt Blue Spinel

Cobalt Blue Spinel Gemstone

Cobalt blue spinel is a rare and highly valued gemstone known for its vibrant blue color, which is primarily attributed to the presence of cobalt ions. Here’s a detailed overview of cobalt blue spinel, including its characteristics, origins, and identification methods.

Characteristics

• Color: Cobalt blue spinel exhibits a pure, vivid blue hue, distinguishing it from other blue spinels that may contain iron, which can impart a grayish or greenish tint. The intensity of the blue color is directly related to the cobalt content; higher concentrations of cobalt yield more saturated blues.
• Composition: While cobalt is the dominant chromophore in cobalt blue spinel, iron may also be present, but in lower amounts. There is no established ratio of cobalt to iron that defines a cobalt spinel, but the key factor is that cobalt must be the primary coloring agent.
• Magnetism and Fluorescence: Natural cobalt blue spinels can exhibit magnetic properties due to the presence of iron. They may also fluoresce pink or red under UV light, which is a characteristic of cobalt.

Origins

Cobalt blue spinels are primarily sourced from specific locations, with notable deposits found in:

• Vietnam: Particularly from the Luc Yen region, which is recognized for producing some of the most vivid cobalt blue spinels.
• Tanzania: This region is also known for its high-quality cobalt blue spinels, often marketed for their electric blue color and clarity.

Identification

Identifying cobalt blue spinel can be complex due to the similarities with other blue gemstones. Here are some methods used by gemologists:

• Spectroscopic Analysis: A spectrometer can reveal the absorption spectrum of the stone, helping to determine whether cobalt is the primary coloring agent. Cobalt exhibits distinct absorption features compared to iron.
• Magnetic Testing: Natural cobalt blue spinels typically show some magnetic attraction due to iron content, which can help differentiate them from synthetic counterparts that do not exhibit this property.
• Fluorescence Testing: Under long-wave UV light, cobalt blue spinels will fluoresce, which can be a useful identification tool in gemology.

Market Value

The value of cobalt blue spinel can vary significantly based on its size, color saturation, and clarity. Prices can range from $2,000 to over $10,000 per carat for high-quality specimens, reflecting their rarity and desirability in the gemstone market.