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Spinel

The Black Prince’s Ruby. The Timur Ruby. For centuries, spinel, the great imposter, masqueraded as ruby in Europe’s crown jewels.

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Stunning Color

The finest red spinel colors are pure red to slightly purplish red hues of medium to medium-dark tone.

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Cut for Brilliance

Spinel is most often cut in cushion and oval shapes; when properly proportioned it has excellent brilliance.

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Chromium

Like ruby, the color of red spinel is due to traces of chromium.

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Nature’s Perfection

Spinel belongs to the cubic crystal system and its characteristic crystal shape is an octahedron, which looks like two back-to-back pyramids.

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Perfect for Jewelry

Like ruby, spinel is found in alluvial deposits; it ranks 8 on the Mohs scale and has good toughness, making it a durable gem for jewelry.

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Collector’s Favorite

Well-formed spinel crystals are in high demand among mineral collectors.

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Tools

Research

A crystal inclusion in red spinel shown in darkfield illumination (left) and fiber-optic lighting (right). Photomicrographs by Isabelle Corvin; field of view 1.78 mm.
Suspended Crystal in Red Spinel

A crystal inclusion in red spinel displays rainbow colors under fiber-optic lighting.

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Stellate dislocations decorate the interior of a greenish blue spinel believed to be from Vietnam. Photomicrograph by Ezgi Kiyak; field of view 4.79 mm.
Large Stellate Dislocation in Spinel

A greenish blue spinel displays a large network of needle-like dislocations clustered in a six-rayed star pattern.

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A precipitation of an unidentified mineral in a fissure of a purple spinel creates this highly intricate moiré pattern. A combination of oblique fiber-optic and darkfield illumination was used. Photomicrograph by Tyler Smith; field of view 2.90 mm.
Fissure with Moiré Pattern in Spinel

A precipitation of an unidentified mineral creates a complex moiré pattern in a fissure of a purple spinel.

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Morphological features of the tourmaline crystal included in the heliodor are visible; striations and triangular growth marks are present. A band of fluid inclusions is visible near the tip of the schorl tourmaline. Photomicrograph by Rhiana Elizabeth Henry; field of view 2.90 mm. Gift of Mark Mauthner, GIA Museum no. 37772.
Heliodor with a Large Schorl Inclusion

An 8.33 ct rectangular heliodor displays two tourmaline inclusions and a thin band of fluids.

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Figure 1. Suite of faceted nickel-diffused spinel (0.67–1.01 ct) showing a range of color from blue to bluish green. Photo by Aaron Palke and Diego Sanchez.
Color Modification of Spinel by Nickel Diffusion: A New Treatment

Reports on a newly discovered treatment process for producing a deep blue color in natural spinel and proposes identification criteria.

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Figure 1. This faceted purple spinel, weighing 0.51 ct and measuring 5.20 × 4.17 × 3.10 mm, was reportedly from Tanzania. Photo by Jinlin Wu.
Forsterite in a Purple Tanzanian Spinel

Examination of a purple spinel from Tanzania reveals a rare forsterite inclusion.

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Figure 1. Suite of faceted nickel-diffused spinel (0.674–1.009 ct) showing the range of color from blue to bluish green. Photo by Aaron Palke and Diego Sanchez.
Article
Color Modification of Spinel by Nickel (Ni) Diffusion: A New Treatment in the Gem Market

GIA researchers report on a new nickel-diffusion treatment used to modify color in spinel and present criteria for identification.

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Figure 1. This 1.01 ct gahnospinel had an intense “cobalt blue” color. Photo by Lhapsin Nillapat.
A “Cobalt Blue” Gahnospinel

Cobalt is identified as the primary coloring agent in an intense blue specimen of gahnospinel at GIA’s Bangkok laboratory.

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A 20 ct faceted spinel from the Kul-i-Lal deposit of Tajikistan.
Color Mechanism and Spectroscopic Thermal Variation of Pink Spinel Reportedly from Kuh-i-Lal, Tajikistan

A detailed spectroscopic investigation of the color of pink spinel reportedly from the Kuh-i-Lal deposit in the Pamir Mountains of Tajikistan.

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Iridescent needles in a Vietnamese red spinel resemble a skyline.
Vietnamese Skyline

Red spinel from Vietnam features iridescent needles resembling a futuristic skyline.

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