The facts
What esperite actually is
Mineralogically, esperite is lead-zinc silicate — PbCa₃Zn₄(SiO₄)₄, crystallising in the monoclinic system.
The colour is caused by white in daylight; brilliant lemon-yellow short-wave fluorescence. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.760–1.774, and the specific gravity sits near 4.28–4.42; cleavage is good in one direction.
Where esperite comes from
The recognised sources are Franklin Mine, Sussex County, New Jersey, USA.
One source only — which is unusual, and which means an origin claim naming anywhere else is either a mistake or a different material.
How esperite is treated
Untreated. Essentially a Franklin-only species prized for fluorescence; not cut as a gem.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What esperite is confused with
The usual confusions are Willemite, Calcite and Hardystonite.
The separation is rarely a matter of opinion: refractive index 1.760–1.774 and specific gravity 4.28–4.42 settle most of it in a minute, and magnification settles the rest.
What esperite is used for
Esperite is bought by mineral collecting and decorative objects — and each of those trades wants a different form of the same material.
We quote each application in the unit that trade actually buys in, by the specimen or by the piece.
Durability and care
Hardness 5–5.5; cleavage good in one direction. That combination decides what it can safely be set into.
Below about 5.5 a stone will be scratched by ordinary household dust, which is largely quartz. That does not make it unusable — it makes it a pendant, an earring or an object rather than a ring worn every day.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What esperite costs
Indicative pricing for esperite is Specimens 60–800 USD.
That is a range, not a quote. Colour, size, clarity, cut and origin move the figure a long way inside it, and the only honest price is one given against a specific stone. Send us what you need and we will price it.
Questions
Is esperite treated, and how?
Untreated. Essentially a Franklin-only species prized for fluorescence; not cut as a gem.
Where does esperite come from?
Franklin Mine, Sussex County, New Jersey, USA. That is the only commercial source.
Is esperite hard enough to wear every day?
Not really. At 5–5.5 on the Mohs scale it is softer than the quartz dust in ordinary household dirt, so it scratches with wear. It suits pendants, earrings and objects better than a daily ring.
How much does esperite cost?
Indicatively Specimens 60–800 USD. Colour, size, clarity and origin move the price a long way within that, so treat it as a range and ask for a quote against a specific stone.
What is esperite confused with?
Most often Willemite, Calcite and Hardystonite. A refractive index of 1.760–1.774 and a specific gravity near 4.28–4.42 separate it quickly.
Related stones
Looking for esperite?
Tell us the size, the quality and what it is for. We source it, photograph it and quote it — with the locality named.
Ask about esperite