Datolite
Datolite is a calcium borosilicate mineral crystallizing in the monoclinic system, typically found as glassy, pale green to colorless crystals or as compact, porcelain-like nodules infilling cavities in basalt. It forms primarily through low-temperature hydrothermal activity following the cooling of basaltic lava flows. Its association with native copper deposits in Michigan's Keweenaw Peninsula has made it a favorite among mineral collectors in the region.
Datolite properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | CaBSiO4(OH) |
| Mohs hardness | 5–5.5 |
| Crystal system | Monoclinic |
| Luster | Vitreous, slightly greasy |
| Streak | White |
| Cleavage | Poor/indistinct |
| Fracture | Conchoidal |
| Specific gravity | 2.9–3.0 |
| Transparency | Transparent to translucent |
| Common colors | Colorless, White, Pale green, Yellow, Pink |
| Rarity | common |
Geology & background
Datolite crystallizes when silica- and boron-bearing hydrothermal fluids circulate through gas cavities, or vesicles, in cooling basalt flows, gradually filling the pockets with glassy crystal linings or dense, opaque nodules. The Lake Superior copper district of Michigan is world-famous for datolite, where it occurs intergrown with native copper in dramatic combination specimens that command high prices among mineral collectors. Other notable localities include Westfield, Massachusetts, and various trap rock quarries throughout New Jersey and Connecticut.
Massive, opaque datolite nodules found in New Jersey trap rock quarries are sometimes cut and polished for cabochons, showing mottled white, pink, or green patterns similar to porcelain. Collectors distinguish between transparent crystallized datolite, valued for its glassy luster and sharp crystal faces, and the massive, cryptocrystalline variety, valued instead for lapidary use. Because datolite from copper districts often contains visible native copper inclusions, combination specimens are especially sought after and priced well above plain crystal examples.
How to identify Datolite
Datolite typically appears colorless, pale green, yellow, or pink, with a vitreous, glassy luster on well-formed crystal faces, though massive nodular material can look dull and porcelain-like. Its streak is white, hardness is about 5 to 5.5, and it lacks a well-developed cleavage, breaking instead with a conchoidal fracture typical of glassy minerals. Crystal habit ranges from short, stubby prisms to dense, rounded nodules. It is sometimes confused with prehnite or zeolite minerals found in similar basalt cavities, but datolite's greater hardness and glassier luster set it apart.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Datolite is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Datolite worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Some of the finest datolite specimens combine glassy crystal clusters with visible native copper, a pairing found almost nowhere outside Michigan's Keweenaw Peninsula.
- Massive datolite nodules are sometimes cut into cabochons that resemble fine porcelain because of their dense, uniform, cryptocrystalline texture.
- Datolite gets its name from the Greek word for divide, a reference to its granular fracture pattern noted by the mineral's original describer.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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