Ruby Red Spinel Floater
Magnesium Aluminum Oxide, MgAl2O4
Crystal System: Cubic
- Spinel occurs as an accessory mineral in igneous rocks such as gabbro. Spinel is the
name of a series rather than a specific mineral. It also occurs in in contact
metamorphic rocks, especially marly dolomitic limestones rich in magnesium and aluminum,
where it is associated with phlogopite, graphite and chondrodite. Due to it's hardness
and resistence to weathering, spinel occurs commonly in alluvial and marine placers.
- Spinel crystals occur as transparent to opaque octahedrons which are commonly twinned.
It's color is quite variable, ranging through black, red, blue, green, brown, and
colorless. Iron, zinc and manganese atoms can substitue for magnesium in its structure,
causing variations in color and physical properties.
- While magnetite, chromite and ganhite are all members of the spinel group, the
characteristic gem spinel excludes these minerals. The group of spinels used as gem
stones are transparent and often of attactive color. The most usual colors seen are ruby
red and rose red.
- Stuart provides the following remarks:
- "This is four views of one large floater Spinel octahedron from the ancient locality of
Mogok, Burma (currently known as Myanmar). It has very fine deep "ruby" red color and
measures 1 inch on each edge."
Rocks from Stuart Wilensky's Collection
Index of Specimen Images
Table of Contents