11.21-ct purpurite, pear-shape cabochon, Namibia. Photo courtesy of liveauctioneers.com and Jasper52.
Purpurite is too soft for jewelry wear and never transparent. Nevertheless, lapidaries have cut cabochons from this material with magnificent purplish rose hues.
| Data | Value |
|---|---|
| Name | Purpurite |
| Formula | (Mn,Fe)PO4 |
| Colors | Deep rose to reddish purple; alters on outside to brown or black. |
| Fracture | Uneven |
| Hardness | 4-4.5 |
| Cleavage | Good 1 direction |
| Crystallography | Orthorhombic. Crystals rare, in small masses and cleavages. |
| Refractive Index | 1.85-1.92 |
| Birefringence | 0.007 |
| Dispersion | Very strong |
| Luminescence | None |
| Luminescence Present | No |
| Absorption Spectrum | Not diagnostic |
| Pleochroism | Strong: gray/rose-red or deep red/purplish red. |
| Optics | a = 1.85; β = 1.86; γ = 1.92. Biaxial (+), 2V moderate. |
| Optic Sign | Biaxial + |
| Luster | Dull, satiny. |
| Specific Gravity | 3.69 |
| Enhancements | Acid etching |
| Transparency | Translucent to opaque |
| Etymology | After the Latin purpura for "purple," in allusion to the color. |
| Occurrence | A secondary mineral, due to the oxidation of phosphates in granite pegmatites. |
Purpurites (about 2 inches across), Usakos, Namibia. Photo © Joel E. Arem, PhD, FGA. Used with permission.
Purpurite forms a mineral series as the manganese-dominant (Mn) end member to the iron-dominant (Fe) end member heterosite. Both end members have similar colors and properties, but purpurites occur far more rarely than heterosites.
Heterosite, 11.7 x 5.4 x 5.4 cm, Newry, Oxford Co., Maine, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.
Sugilites and charoites can look like purpurites and show the same purple colors. Keep in mind that purpurite is the rarest of these three gem materials and is also the least likely to be found cabbed or carved.
Despite appearances, there are numerous differences between these materials. Purpurite has a much higher, over-the-limit refractive index. Physically, purpurite has a softer hardness (4-4.5) than sugilite (6-6.5) and charoite (5-6) as well as a purple streak. Sugilite and charoite have white streaks. However, scratch and streak tests aren’t recommended for finished gemstones.
The easiest way to distinguish these gems is a specific gravity (SG) test. Purpurite has a much greater SG value (3.69) than sugilite (2.74) and charoite (2.54-2.78).
Scientists have synthesized purpurites for mineralogical research. However, despite purpurite’s rarity and attractive color, it’s unlikely there is any consumer demand for this lab-created material. This gemstone is too little known to generate much of a market and too soft for jewelry wear.
Mineral specimens may receive acid treatments to enhance their purple color.
A purpurite mass on quartz, lightly treated with oxalic acid to brighten it. Brown Thurston prospect, Rumford, Oxford County, Maine, USA. Photo by Douglas Watts. Licensed under CC By 3.0.
Usakos, Namibia produces rich, purplish masses in abundance and at low cost. Most gem-quality material comes from this location.
Other notable sources include the following
Purpurite on matrix, Bendada Mine, Bendada, Sabugal, Guarda, Portugal. Photo by Pascal Ollic. Public Domain.
Cabochons up to several inches long can be cut from cleavages.
Avoid cleaning purpurites with mechanical cleaning systems, like steam and ultrasound. Clean these gemstones only with a soft brush, mild detergent, and warm water. Consult our gemstone jewelry cleaning guide for more care recommendations.
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