Relatively unknown to the public, spinel comes in virtually every possible color. Red is
the most common, with many fine examples of blue, violet and green, but it is also found
in orange, brown, pink, yellow, black, and colorless. Occasionally star spinel will be
found. Spinels will have lively color and few inclusions and will rarely be found larger
than 5 carats. Red spinel, sometimes referred to as a Balas Ruby, has often been confused
for the ruby. The best example of this mistaken identity being in the English Crown Jewels,
where two large spinels that have been thought to be rubies for centuries. Like ruby, red
spinel exhibits fluorescence, or a glow, in natural light. To make the gem even harder to
distinguish from corundum, it is generally found in the same gravel deposits as corundum
and share similar physical characteristics. A good red or blue spinel will command prices
at the top of the secondary market, but not anywhere near to that of a ruby or sapphire.
The finest and most famous examples of red and pink stones are from Myanmar while the
greatest production of spinel is from the gem gravel of Sri Lanka and Thailand. These
stones tend to be somewhat paler than their counterparts from Myanmar. Spinel is also
found in the USA, Brazil, Australia, Afghanistan, Pakistan, Tajikistan, Cambodia,
Tanzania, Sweden, and Russia. Although it is much less expensive, fine spinels are now
more rare than the rubies they used to imitate. The old mines of Afghanistan where many
of the giant stones were discovered have been worked out and the gem gravels that once
produced the finest specimens in southern Asia now produce few gems with the color and
intensity of gems once found there.
| Composition | MgAl2O4 | Class | Oxide |
| Specific gravity | 3.54 - 3.63 | Refractive Index | 1.712 - 1.762 |
| Birefringence | None | Pleochroism | None |
| Cleavage | indistinct | Fracture | conchoidal, uneven |
| Luster | vitreous | Transparency | transparent to opaque |
| Streak | white | Fluorescence | Red: strong red, Blue: weak reddish or green |
| Crystal system | Cubic | Twinning | common |
| Hardness | 8 | Dispersion | .020 |
| Color | red, pink, orange, yellow, green, blue, purple, black, brown, and colorless. |
| Source | Burma, Sri Lanka, Brazil and Afghanistan |
| Crystal habit | typically octahedron, but can be found as dodecahedrons and combinations of other isometric forms |
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Spinel was recognized as a distinct species of gem in 1587 in Burma (Myanmar), but was
not recognized globally for several hundred years. The earliest known use of spinel was
from about 100 BC in a Buddhist tomb in Afghanistan, and was used in jewelry by the
Romans. Mining for spinel was first seen in Afghanistan about the year 750 AD. This same
region produced the largest gemstone of 412 carets. The origin of the name spinel is
unclear, but may have come from Latin spina meaning a thorn, or from the Greek word
meaning a spark.
Spinel, like garnet and tourmaline, is a mineral name that refers to a group of minerals
all having the same crystal structure. Members within the group differ by containing
varying amounts of Cr, Fe, Mn, Ni, and Zn that substitute for Mg and Al in the crystal
structure. The most familiar minerals that have the spinel crystal structure are
the ore minerals magnetite (Fe2+Fe3+2O4) and chromite (Fe2+Cr2O4), neither of which is a
gem material. Red and pink spinel is colored by trace quantities of Cr; blue, violet,
orange and green by Fe. Zn, Cr, and Co (rare) are also present in some blue, violet and
purple stones.
