Herderite Value, Price, and Jewelry Information
Herderite is a rare collector's gem, especially in larger sizes. It's too soft for wear but attractive when cut and can show a wide range of colors.
Herderite Value
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
Herderite Information
| Data | Value |
| Name | Herderite |
| Crystallography | Monoclinic. Crystals stout or prismatic; tabular; crusts. |
| Refractive Index | 1.591-1.624 |
| Colors | Colorless, pale yellow, greenish white, pink, green, violet. |
| Luster | Vitreous. |
| Fracture | Conchoidal |
| Hardness | 5 - 5.5. |
| Specific Gravity | 2.95-3.02 |
| Birefringence | 0.028-0.030. |
| Cleavage | Indistinct, Interrupted on {110} |
| Dispersion | 0.017 |
| Luminescence | Pale green in LW and SW; also stronger violet in LW. Orange fluorescence in X-rays with persistent phosphorescence. |
| Transparency | Translucent to transparent. |
| Absorption Spectrum | Not diagnostic. |
| Formula | CaBePO4(F,OH). |
| Pleochroism | None or weak. |
| Optics | a = 1.591-1.594; β = 1.611-1.613; γ = 1.619-1.624. Biaxial (- or +), 2V = 67-75°. See “Identifying Characteristics” below. |
| Etymology | After S. A. W. von Herder, a mining official in Freiburg, Germany (1776–1838). |
| Occurrence | Late stage hydrothermal mineral in granite pegmatites. |
Comments
Herderite belongs to the herderite-hydroxylherderite mineral series as the fluorine (F)-dominant end member. If hydroxyl (OH) dominates, the specimens are then called hydroxylherderites. Herderites are rarer than hydroxylherderites, and some gems may be misidentified as their hydroxyl-dominant brethren.
Clean and large stones are very hard to find. However, more gem material may come on the market from Brazilian sources.
Identifying Characteristics
Some herderites can have a biaxial (+) optic sign. In general, however, OH-dominant specimens will have a positive sign. F-dominant specimens will have a negative sign.
The refractive indices (RI) of these gems systematically decrease as their F content increases. Thus, RIs in the lower range may indicate herderites.
The green gem from Brazil in Dr. Arem’s photo (above, right), has the following properties:
- RI: a = 1.581; β = 1.601; γ = 1.610.
- Birefringence: 0.029.
- Specific Gravity: 3.02
- Luminescence: Pale violet in shortwave (SW).
- Contains 7% F.
Synthetics
No known synthetics or enhancements.
Sources
Brazil and Pakistan yield gem-quality herderites as well as hydroxylherderites. Minas Gerais, Brazil has produced crystals up to nearly fist size. Their colors include colorless and pink as well as some green and violetish.
The following locations may produce hydroxylherderites.
- United States: Maine (colorless and pale yellow crystals); New Hampshire.
- Austria; Germany; Russia.
Stone Sizes
Faceted gems from Maine usually range in size from 1 to 5 carats. They usually show pale colors or appear colorless. Herderites from Brazil, however, have stronger colors. Faceters may cut stones up to 25 or 30 carats from larger crystals.
- Smithsonian Institution (Washington, DC): 5.9 (green, Brazil).
- Devonian Group (Calgary, Alberta, Canada): 3.65 (blue, Brazil).
- National Museums of Canada (Ottawa, Ontario): 4.65 (light violet octagon, Brazil).
Care
Due to their relatively low hardness (5 – 5.5), don’t clean herderites through mechanical processes, such as steam or ultrasonic systems. Instead, use a soft brush, mild detergent, and warm water. Avoid storing them with other harder, more common gemstones to avoid contact scratches. Consult our gemstone jewelry cleaning guide for more recommendations.
