Analcime
Analcime is a hydrated sodium aluminosilicate, NaAlSi2O6·H2O, and one of the few zeolites to crystallize in the isometric system rather than a lower-symmetry one. It typically forms trapezohedral crystals with twenty-four faces, giving specimens a distinctive rounded, many-sided appearance. Chemically it sits at the boundary between the zeolite and feldspathoid mineral groups.
Analcime properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | NaAlSi2O6·H2O |
| Mohs hardness | 5–5.5 |
| Crystal system | Isometric |
| Luster | Vitreous |
| Streak | White |
| Cleavage | Poor, indistinct cubic |
| Fracture | Conchoidal to uneven |
| Specific gravity | 2.24–2.29 |
| Transparency | Transparent to translucent |
| Common colors | Colorless, White, Gray, Pink, Pale green |
| Rarity | common |
Geology & background
Analcime most commonly lines gas cavities in basalt and related volcanic rocks, crystallizing from silica- and sodium-rich fluids as lava cools, often alongside other zeolites such as natrolite and stilbite. It also forms as a primary mineral in sodium-rich igneous rocks like analcime basalt and teschenite, and as a secondary mineral in saline, alkaline lake sediments where volcanic glass alters in contact with sodium-carbonate brines. Notable vesicle-lined specimens come from Milos in Greece, the basalts of Nova Scotia's Bay of Fundy, and India's Deccan Traps. For collectors, the trapezohedral crystal habit is often the fastest identifying feature, since few other minerals form such rounded, near-spherical crystals inside basalt cavities. Analcime is soft enough to scratch with a knife and can be mistaken for leucite, though leucite forms in potassium-rich volcanic rocks rather than basaltic vesicles and lacks analcime's structural water.
How to identify Analcime
Analcime forms colorless, white, or pale pink trapezohedra with rounded, many-faced outlines, sometimes resembling small soccer balls. Luster is vitreous to slightly greasy, streak is white, and hardness runs 5 to 5.5. It lacks cleavage and breaks with a conchoidal fracture. Because it shares vesicle-filling habits with other zeolites, crystal shape is the most reliable clue; leucite looks similar but occurs in potassium-rich lavas rather than basalt cavities.
- 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 Analcime is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Analcime 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
- Analcime's nearly spherical trapezohedral crystals are so symmetrical that they are sometimes mistaken for polished beads rather than natural crystal faces.
- It sits chemically between the zeolites and the feldspathoids, and mineralogists have long debated which family it truly belongs to.
- Some analcime forms not in volcanic rock at all but in ancient alkaline lake beds, cementing sediment as saline water evaporated.
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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