El Hoyazo crater gemstones: rare volcanic garnets and cristobalite, precision-cut by hand.
El Hoyazo (Níjar, Almería, Spain) is the crater of an ancient submarine volcano formed around 10 million years ago. After the volcano became inactive, coral reefs developed along the crater rim—now preserved as fossils. Erosion and sea-level changes have kept this geological structure remarkably well preserved.
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~10 million years ago: the submarine volcano forms.
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The volcano emerges above sea level.
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~6 million years ago: volcanic activity ends and a coral reef begins to form (now fossilized).
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The reef may have formed a true atoll, with a lagoon at the center of the extinct volcano.
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Sea-level drop and erosion leave today’s structure almost intact, with volcanic domes and vents in the center
Current panoramic view of the crater from inside the volcano with its volcanic chimneys in the center and fossilized reefs at the top.
Wich minerals can be found?
Inside the crater you can find a variety of minerals and crystals such as sillimanite, biotite, cordierite, cristobalite and garnets. These crystals come from ancient, deep rocks that the rising magma incorporated and carried to the surface.
Sillimanite
Biotite
Cordierite
Cristobalite
El Hoyazo garnets: what they are like?
Most crystals are small garnets ranging from 1 mm to 1.5 cm (mainly almandine/andradite types). They often occur as well-formed cubic crystals—octahedra, rhombic dodecahedra, trapezohedra, or combinations—typically deep red, but commonly fractured and included. Because of their hardness and overall low quality, El Hoyazo garnets have historically been used for abrasives.
They can be found embedded in, or released from, their host rock: dacites, fine-grained volcanic rocks formed from relatively acidic, viscous magmas.
Garnet crystal in Dacite
Detached garnets of abrasive quality.
Do gem-quality garnets occur here?
Yes but they are extremely rare. Roughly one in a thousand shows true gem quality: high transparency and a fine, intense red. With enough searching (and a bit of luck), you may find a genuine treasure that can be cut into a unique gemstone.
Gem-quality garnets
Gem-quality garnet
Why are they so difficult to cut?
Before choosing a cut, a small “window” is polished to examine the interior. Most crystals are fractured or included, and only a few pieces contain a clean enough area to justify faceting. The amount of rough suitable for fine gemstones is extremely limited, which is why these gems are rare and highly valued.
Rough and faceted garnet
Cristobalite from El Hoyazo
High-quality cristobalite from El Hoyazo can also be faceted. Some crystals show exceptional transparency, ranging from a few millimeters up to 10 cm. Cristobalite is a silica polymorph found in volcanic rocks; once cut, it can display an excellent crystal appearance.
Gem-quality cristobalite.
Cut cristobalite
Faceted garnets and cristobalites from the Hoyazo crater
Cristobalite 7.5 x 5.3 mm 1.50 Ct
Garnet 5 mm 0.75 Ct
Garnet and cristobalites ring
Garnet 9.0 x 4.5 mm 0.90 Ct
Garnet 4.3 mm 0.42 Ct
Cristobalite 6 x 4 mm 0.75 Ct
Natural gemstones and delivery
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Natural gemstones, no treatments
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Insured shipping / returns accepted
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Gemological certificate included
