Freeform step-cut ludlamite, 1.35 cts, 9 x 6.7 mm, Blackbird Mine, Salmon, Lehmi Co., Idaho. © The Gem Trader. Used with permission.
Ludlamite has a lovely green color, but cut stones are extremely rare. Large crystals of this phosphate mineral are known from only a few localities.
| Data | Value |
|---|---|
| Name | Ludlamite |
| Formula | Fe3(PO4)2 · 4H2O |
| Colors | Apple green, dark green, pale green, greenish white, colorless. |
| Fracture | Conchoidal |
| Hardness | 3.5 |
| Cleavage | Perfect 1 direction |
| Crystallography | Monoclinic. Crystals tabular, wedge-shaped; also granular. |
| Refractive Index | 1.650-1.697 |
| Birefringence | 0.038-0.044 |
| Luminescence | None |
| Luminescence Present | No |
| Absorption Spectrum | Not diagnostic |
| Pleochroism | None |
| Optics | a = 1.650-1.653; β = 1.667-1.675; γ = 1.688-1.697. Biaxial (+), 2V= 82°. |
| Optic Sign | Biaxial + |
| Luster | Vitreous |
| Specific Gravity | 3.19 |
| Transparency | Translucent to transparent |
| Etymology | After Henry Ludlam, English mineralogist and collector. |
| Occurrence | A secondary mineral in the oxidized zone of ore deposits; also due to the alteration of primary phosphates in granite pegmatites. |
Gemmy ludlamites on quartz, 7.2 x 4.7 x 4.7 cm, Wheal Jane, Baldhu, Gwennap area, Camborne – Redruth – St Day District, Cornwall, England, UK. © Rob Lavinsky, www.iRocks.com. Used with permission.
In addition to beautiful color, ludlamites can show great brightness when faceted into gemstones. Unfortunately, this mineral occurs very rarely and even more rarely in cuttable sizes. They also have a hardness of only 3.5 and perfect cleavage. This makes ludlamite difficult to cut and impractical to wear as a jewelry stone. As a ring stone, it would need a protective setting and would be best reserved for occasional wear only. Use for earrings, pendants, and brooches would be more advisable.
However, you’re more likely to find ludlamites in mineral collections, if at all, than in jewelry collections.
Shield-cut ludlamite, 0.26 cts, 5.2 x 2.7 mm, Blackbird Mine, Lemhi Co., Idaho. © The Gem Trader. Used with permission.
Chemically similar, vivianite can occur in the same sources as ludlamite. When exposed to light, colorless and pale green vivianites can turn dark green as well as blue. Thus, some of these stones may look alike. Nevertheless, gemologists can distinguish them with some basic tests.
Ludlamites have a higher refractive index and specific gravity (1.650-1.697 and 3.19) than vivianites (1.569-1.675 and 2.64-2.68). Vivianites can also show dramatic pleochroic colors, but ludlamites have no pleochroism.
These gems also have different physical properties. Vivianites have a much lower hardness (1.5 to 2) than ludlamites. Vivianites also have a streak that can range from colorless to blue. Ludlamites have a pale, greenish white streak. However, scratch and streak testing are not recommended for finished gems.
Both gems are rarely cut, but vivianite is cut far less often than ludlamite.
There are no known lab-created ludlamites. These gems usually receive no treatments or enhancements.
The most celebrated source for gem-quality ludlamite, Blackbird Mine, Lemhi County, Idaho produces fine crystals up to a ½ inch across.
Other notable sources include the following:
Cluster of ludlamites, 3.0 x 2.6 x 1.7 cm, San Antonio Mine, Santa Eulalia, Chihuahua, Mexico. © Rob Lavinsky, www.iRocks.com. Used with permission.
Transparent ludlamite material is always small. The potential may exist for cutting 5-10 carat gems, but most finished stones usually range from 1 to 2 carats or smaller.
Avoid cleaning ludlamites 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.
Ludlamite: Idaho (~0.5). Photo © Joel E. Arem, PhD, FGA. Used with permission.
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