Herderite Value, Price, and Jewelry Information

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Herderite, 6.92-ct, 12.7 x 10.5 x 6.0 mm, green, Brazil. © ARK Rare Gems. Used with permission.

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 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.
Hardness	5 - 5.5.
Fracture	Conchoidal
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.
Luminescence Present	Yes
Luminescence Type	Fluorescent, Phosphorescent, UV-Long, UV-Short, X-ray Colors
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.
Optic Sign	Biaxial +, Biaxial -
Etymology	After S. A. W. von Herder, a mining official in Freiburg, Germany (1776–1838).
Occurrence	Late stage hydrothermal mineral in granite pegmatites.

Herderite: Brazil (9.6, 3.65, 9.25). Photo © Joel E. Arem, PhD, FGA. Used with permission.

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.

“Hydroxylherderite,” Bennett Quarry, Buckfield, Oxford Co., Maine, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.

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.