The facts
What lake Superior Agate actually is
Mineralogically, lake Superior Agate is chalcedony (agate) — SiO₂, crystallising in the cryptocrystalline trigonal system.
The colour is caused by iron oxide from the surrounding basalt gives the characteristic rust-red and orange fortification bands. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.530–1.539, and the specific gravity sits near 2.58–2.64; cleavage is none.
Where lake Superior Agate comes from
The recognised sources are North Shore of Lake Superior, Minnesota, USA and Keweenaw Peninsula, Michigan, USA.
Origin affects price in this material, so we name the locality on every quote rather than the country. "African" or "Asian" tells a buyer nothing.
How lake Superior Agate is treated
Untreated. Glacially transported from Keweenawan basalt flows, so nodules are found in gravel far from their source. Water-worn skin is prized and should not be polished away.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What lake Superior Agate is confused with
The usual confusions are Fairburn agate, Moss agate and Carnelian.
The separation is rarely a matter of opinion: refractive index 1.530–1.539 and specific gravity 2.58–2.64 settle most of it in a minute, and magnification settles the rest.
What lake Superior Agate is used for
Lake Superior Agate is bought by mineral collecting, jewellery 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, by the carat or by the piece.
Durability and care
Lake Superior Agate is 6.5–7 on the Mohs scale, with none cleavage.
With no cleavage plane to worry about, the practical limit is abrasion rather than breakage, and it takes daily wear well.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What lake Superior Agate costs
Indicative pricing for lake Superior Agate is Tumbled stones 2–20 USD; fine banded specimens 50–500 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 lake Superior Agate treated, and how?
Untreated. Glacially transported from Keweenawan basalt flows, so nodules are found in gravel far from their source. Water-worn skin is prized and should not be polished away.
Where does lake Superior Agate come from?
North Shore of Lake Superior, Minnesota, USA and Keweenaw Peninsula, Michigan, USA. Origin affects price, so we name the locality rather than the country on every quote.
Is lake Superior Agate hard enough to wear every day?
Yes. At 6.5–7 on the Mohs scale with no cleavage plane, it handles daily wear well. The practical limit is gradual abrasion rather than chipping.
How much does lake Superior Agate cost?
Indicatively Tumbled stones 2–20 USD; fine banded specimens 50–500 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 lake Superior Agate confused with?
Most often Fairburn agate, Moss agate and Carnelian. A refractive index of 1.530–1.539 and a specific gravity near 2.58–2.64 separate it quickly.
What is lake Superior Agate used for besides jewellery?
mineral collecting and decorative objects. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for lake superior agate?
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 lake superior agate