Not a single species

“Lava stone” is vernacular, not a formal rock name. In collections and bead trays, it usually means vesicular basalt (scoria)—a basaltic lava packed with gas bubbles. In landscaping and construction, the same material is often called cinder or scoria.

Related volcanic textures

Pumice is the frothier, silica‑rich cousin that can float. Obsidian is volcanic glass with little to no vesicles. All are volcanic, but their chemistry and gas content differ.

Gas dissolved in magma

Magmas carry dissolved gases (H₂O, CO₂, SO₂). As pressure drops near the surface, gases exsolve—they form bubbles, like opening a fizzy drink.

Freezing the fizz

In fluid basaltic lavas, bubbles rise and expand while the melt cools. If the lava solidifies quickly, the bubbles are trapped as vesicles. Where bubbles burst and walls collapse, you see ragged openings and thin partitions.

After the eruption

Mineral‑rich fluids later may infill vesicles with secondary minerals like calcite, zeolites, quartz, prehnite, or chlorite—these filled bubbles are called amygdales, and the rock becomes amygdaloidal basalt.

Palette & surfaces

• Black to charcoal — most common for basaltic scoria.
• Gray — weathered surfaces and silica‑richer lavas.
• Reddish‑brown — iron oxidation near air‑exposed cinder cones.

Vesicles range from pinpricks to marble‑size. Walls are often sharp and angular; tumbled beads feel pleasantly matte.

Flow textures (bonus)

• Pāhoehoe — smooth, ropy surfaces; vesicles can line flow tops.
• ‘A‘ā — clinker‑like, rubbly flows; scoria fragments dominate.
• Spatter / bombs — droplet‑shaped pieces with stretched vesicles.

Photo hint: Side‑light at ~30° makes vesicle edges cast tiny shadows, revealing the foam‑like architecture.

Vesicles & amygdales

Look for rounded to irregular cavities with glassy, crystalline, or earthy linings. If infilled, you may see calcite, zeolites, chalcedony, prehnite, or quartz forming tiny geodes.

Phenocrysts & microlites

Small, sharp crystals of plagioclase (white), pyroxene (dark), or olivine (greenish) may sit in a fine groundmass. Microlites align with flow, creating subtle streaks.

Oxidation fringes

Rusty red halos around vesicles reflect iron oxidation along pore walls—common in scoria exposed to air and steam during eruption.

Global stage

Wherever volcanoes breathe: Iceland, the Hawaiian Islands, Canary Islands, Italy (Etna, Stromboli), the Eifel (Germany), the East African Rift, and volcanic arcs and fields worldwide.

Classic cones

Cinder cones like Parícutin (Mexico) and fields around Flagstaff, Arizona are textbook scoria factories—thousands of meters of ash and lapilli peppered with vesicular fragments.

Slag (industrial)

Glassier, often with metallic sheen or elongated vesicles; may show swirls and man‑made flow textures. Context (near foundries/railways) helps.

Dyed porous stones

Some porous limestones or ceramic beads are dyed black to mimic lava. Under magnification, dye pooling in pores and a uniform, “painted” look are clues.

Obsidian

Volcanic glass with no vesicles (unless a “pumiceous” variety). Breaks with sharp conchoidal fractures and high glassy luster—quite different hand feel.

Scoriaceous andesite

Intermediate‑composition vesicular lava can look similar but may trend grayer with more plagioclase phenocrysts. Chemistry confirms the difference.

Quick checklist

• Abundant, rounded to ragged vesicles.
• Dark mafic palette; often weakly magnetic.
• Matte feel when tumbled; gritty where fresh.

Fun magnet test

A small magnet may tug slightly due to magnetite grains. It won’t stick like to pure iron, but you’ll often feel a faint pull.

Porous reality

• Vesicles collect dust and liquids; a soft brush and mild soap help.
• Rinse and dry; avoid long soaks that can lodge residues deep inside.

Heat & shock

• Basalt handles heat better than many rocks, but rapid thermal shock can spall edges.
• If heated, let it cool gradually to be kind to micro‑fractures.

Surface & storage

• Matte finishes can pick up oils; wipe with a clean, dry cloth.
• Store separately from very hard minerals to keep edges crisp.

Everyday materials

Vesicular basalts and scoria are used as lightweight aggregate, landscaping stone, barbecue rocks, and drainage media. The low density and rough surface make them practical wherever porosity helps.

Beads & craft

“Lava stone” beads are typically tumbled scoria. The pores create a tactile, matte aesthetic. Under a loupe you’ll see true volcanic vesicles rather than machined pits—each bead is effectively a tiny piece of eruptive history.