metamorphic
Blue Spinel on Marble with Phlogopite
MgAl2O4 (Spinel) in CaCO3 (Calcite/Marble) matrix
Blue Spinel: Hardness 8.0, Vitreous luster, Octahedral crystal habits; Matrix: White marble (hardness 3), with sub-metallic brown Phlogopite mica flakes; Specific gravity 3.5-4.1 for spinel.
Identified More metamorphic →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Blue Spinel: Hardness 8.0, Vitreous luster, Octahedral crystal habits; Matrix: White marble (hardness 3), with sub-metallic brown Phlogopite mica flakes; Specific gravity 3.5-4.1 for spinel.
Formation & geological history
Formed through contact or regional metamorphism of magnesium-rich limestones (dolomites) during the Paleozoic or Mesozoic eras. High heat and pressure transform the limestone into marble while trace minerals crystalize into spinel and mica.
Uses & applications
Primarily used as high-end collector specimens. Gem-quality blue spinel is rare and used in jewelry as a durable alternative to sapphire; the matrix specimens are prized for aesthetic display.
Geological facts
Spinel was for centuries confused with ruby and sapphire. Famous historical 'rubies,' such as the Black Prince's Ruby in the British Imperial State Crown, are actually red spinels. Blue spinel owes its color to trace amounts of cobalt or iron.
Field identification & locations
Identify by looking for small, octahedral-shaped dark blue crystals embedded in a soft, white, granular marble matrix. Most commonly sourced from Luc Yen, Vietnam or the Mogok Valley, Myanmar. Collectors should look for sharp crystal faces and deep color saturation.
More like this
