TABUCHI
STONE JOURNAL

MATERIAL / GEOLOGY

How is stone born?

From magma to rock. Discover a stone through its crystals.

Crystals visible on a split Aji stone surface

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01 / FORMATION

Crystals grow deep underground.

Aji stone is granite, a plutonic rock formed as magma cooled slowly underground rather than erupting as lava. Quartz, feldspar and mica contribute to its character.

Where and how quickly magma cools influences its texture. Slow cooling at depth allows crystals to grow; rapid cooling near the surface can produce fine-grained or glassy material.

HOW ROCKS ARE BORN

How does stone come into being?

Slide sideways to explore their origins →

RocksROCKS
01 / COOLING

Magma cools and solidifies.

Igneous rocks

Plutonic rocks

Cool slowly, deep underground

  • GraniteAji stone belongs here
  • Diorite
  • Gabbro

Volcanic rocks

Cool rapidly, near the surface

  • Rhyolite
  • Andesite
  • Basalt
  • Obsidian
02 / DEPOSITION & TRANSFORMATION

Sediment accumulates. Existing rock transforms.

Origins other than the cooling of magma

Sedimentary rocks

Sand, gravel and biological material accumulate

  • Sandstone
  • Conglomerate
  • Limestone
  • Chert

Metamorphic rocks

Existing rock changes under heat or pressure

  • Marble
  • Gneiss
  • Schist

Representative rocks grouped by how they form. Metamorphic rocks can originate from igneous, sedimentary and other rocks.

03 / EXPOSURE

From deep underground to the surface.

Rock formed underground becomes exposed through uplift and the weathering and erosion of overlying rock. Formation, uplift and erosion each take place over long spans of time.

Aji stone is commonly described as having formed about 80 million years ago, during the Cretaceous. Its story continues in the stone quarried today.

Aji stone extracted from an exposed rock face

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Stone formed underground, extracted at a present-day quarry.

THE INGREDIENTS OF STONE / 07 MINERALS

Seven grains that build stone.

Rocks are gatherings of minerals. Compare seven common types through colour and form.

Common rock-forming minerals — five dark and two light types
GroupMineralTypical colourClues to identification
Dark mineralsDARK / 05BiotiteBIOTITEBlack to dark brownPeels into thin sheets in a consistent direction.
AmphiboleHORNBLENDEBlack to dark greenElongated prisms with oblique cleavage angles.
PyroxenePYROXENEDark green to brownShort prisms with cleavage near right angles.
OlivineOLIVINEYellow-green to greenGranular, with a glass-like lustre.
MagnetiteMAGNETITEIron-blackMetallic lustre; strongly attracted to a magnet.
Light mineralsLIGHT / 02QuartzQUARTZColourless to whiteGlassy lustre; breaks irregularly.
FeldsparFELDSPARWhite to pale pinkSplits along flat planes. A major component of granite.

Colours are representative. Light minerals can appear white or pink. Not all seven minerals occur in Aji stone.

Mineral classification and features: Kurashiki Museum of Natural History / Kokugakuin University Hokkaido Junior College: Science Education Resources

LOOK INTO AJI STONE

A landscape of crystals within grey.

Look closer at a cross-section of Aji stone. Light and dark grains come together to create its character.

Hover to magnify. On mobile, tap “Magnify” and move your finger.
Cut and polished Aji stone, with dark grains among light crystals

Digital magnification of a cut and polished Aji stone surface. Colour alone cannot identify a mineral. Use arrow keys to move and Esc to close.