Calcite‑group cousin

Magnesite belongs to the calcite group of carbonates. Like calcite and dolomite, it builds its structure from rhombohedra and shows perfect rhombohedral cleavage. The chemistry is simple—MgCO₃—but the textures can be complex where it replaces earlier minerals.

Why jewelers meet it often

Natural magnesite’s porous, white canvas accepts dye evenly, making it a frequent stand‑in for turquoise (“dyed magnesite,” sometimes marketed under creative names). It’s also lovely in its own right as clean white beads and cabs with warm tan veining.

Altered ultramafics

In peridotite and dunite terrains, CO₂‑bearing fluids can alter magnesium‑rich rocks (often via serpentine) to magnesite veins and lenses. The result: pale, chalky seams with tan webbing.

Hydrothermal & sedimentary

Magnesite also precipitates from Mg‑rich brines and hydrothermal fluids, forming nodules, concretionary masses, and crusts in cavities.

Replacement textures

Because it often replaces earlier carbonates or silicates, magnesite can inherit ghostly banding or breccia patterns—great visual interest for beads and cabs.

Palette

• Chalk/bone white — the classic look.
• Pale grey — denser pieces and crystalline areas.
• Honey‑tan veins — iron‑stained fractures and healed cracks.
• Dyed blue/green — the well‑known turquoise impersonation.

Finish ranges from matte to a soft satin. High gloss usually involves a light wax/resin sealer due to porosity.

Pattern words

• Spiderweb — thin tan/grey crackle veining.
• Cauliflower — lumpy nodules with concentric growth.
• Brecciated — broken fragments re‑cemented by pale magnesite.
• Porcelain — clean, vein‑free white for minimalist designs.

Photo tip: Neutral, cool light (5000–5600 K) keeps whites crisp. A low raking light at ~25–30° reveals subtle veining without glare.

Veins & pores

Look for tiny pores and soft‑edged tan veins. Dyed stones often show color pooling in those pores and along fractures.

Cleavage flashes

Freshly broken chips show rhombohedral cleavage with a subtle glassy flash—classic carbonate behavior.

Acid hint (on scrap only)

A grain of powder touched with warm, dilute acid will fizz. Do not acid‑test finished jewelry—porosity and dyes won’t thank you.

Howlite

Another white, porous stone often dyed blue. Key differences: howlite is a borate (does not readily effervesce), lighter SG (~2.5), and has a porcelain‑like micro‑texture.

White “turquoise” / “White Buffalo”

Popular trade names; material is typically a magnesite/dolomite‑rich rock, not turquoise. Luster and chemistry differ from true turquoise.

Marble & calcite

Softer (calcite Mohs 3), often crystalline and fizzes readily in cold acid. Magnesite’s effervescence is slower unless warmed/powdered.

Plastic & resin

Very light, warm to the touch, and may show mold seams. A hot pin test (lab only) marks plastic—never do this on real stones.

Dolomite

Another carbonate; usually shows saddle‑shaped crystals in geodes and reacts more sluggishly than calcite, variably like magnesite. Lab tests settle close calls.

Quick checklist

• Matte white with tan veins + soft (≤4.5) + slower cold‑acid fizz → magnesite likely.
• Porcelain‑white, lighter heft, no fizz → think howlite.
• Strong cold‑acid fizz + glassier look → calcite/marble.

Where it turns up

Magnesite is widespread: ultramafic belts and serpentinized terrains, hydrothermal veins, and evaporitic basins. Significant deposits occur in parts of Turkey, China, Greece, Slovakia, Austria, Brazil, and Australia, among others.

Beyond beads

Industrially, magnesite is roasted to make magnesia (MgO) for refractories and specialty cements. In the studio, it’s carved into beads, cabochons, spheres, and often dyed for color play.

Everyday care

• Wipe with a dry or barely damp soft cloth; avoid long soaks.
• Keep away from acids, vinegar, lemon, and harsh cleaners.
• Store separately; quartz, sapphire, and steel can scuff the satin surface.

Jewelry guidance

• Best as pendants, earrings, beads. For rings/bracelets, use protective bezels and mindful wear.
• If dyed, limit sunlight/solvents and avoid ultrasonic/steam cleaning.
• Matte or brushed metal settings enhance the clean, modern white.

On the wheel

• Work cool and gentle; magnesite can undercut along veins.
• Pre‑polish 600→1200→3k; finish with alumina on a soft pad for a satin glow.
• Seal with a thin, reversible microcrystalline wax for stain resistance if a higher sheen is desired.

Fizz test (scrap only)

Place a pinch of powder from a trimming in warm, very dilute acid—watch the slow fizz. It’s a carbonate signature (don’t test finished pieces).

Weight & feel

Compare beads in hand: magnesite feels heftier than howlite, cooler than plastic, and has a gently chalk‑matte feel when unsealed.