TANSO

炭素 — the element of everything

DIAMOND

Carbon, when subjected to the unimaginable pressures of the Earth's mantle — 725,000 atmospheres, temperatures exceeding 1,100 degrees Celsius — undergoes a transformation so complete that it becomes nearly unrecognizable from its origin. The atoms, once loosely bonded in layered sheets, lock into a rigid tetrahedral lattice where each carbon atom bonds to exactly four neighbors. This is diamond: the hardest naturally occurring substance known, transparent where graphite is opaque, insulating where graphite conducts.

The diamond cubic crystal structure is a face-centered cubic Bravais lattice with a two-atom basis. Each unit cell contains 8 atoms. The bond length between adjacent carbon atoms is 1.54 angstroms — the same as in any single C–C bond, yet the three-dimensional repetition of this simple connection creates something that can scratch every other material on Earth.

Diamonds form between 150 and 700 kilometers below the surface, in conditions that have persisted since the Archean eon. They are carried to the surface by volcanic eruptions through narrow pipes of kimberlite and lamproite — a journey that takes hours, through rock that took billions of years to create. Most natural diamonds are between 1 and 3.5 billion years old.

GRAPHITE

The same carbon atoms, given different circumstances, choose a radically different geometry. In graphite, carbon forms planar hexagonal rings — each atom bonded to three neighbors in a flat sheet called graphene. These sheets stack loosely, held together only by weak van der Waals forces, and slide over each other with almost no friction. Where diamond is the hardest material, graphite is among the softest. Where diamond is transparent, graphite absorbs nearly all visible light.

This is the allotrope we touch most often. Every pencil line is a trail of graphene layers sheared from a graphite crystal and deposited onto paper. Writing is, at its most fundamental, a process of leaving carbon behind — a molecular graffiti that our civilization has practiced for centuries with the same element it burns for fuel.

"The same atoms, arranged differently, become either the hardest or the softest."

COMBUSTION

Carbon burns.

This is the reaction that built civilization and may end it. One carbon atom meets two oxygen atoms at sufficient temperature, and the bond that forms releases energy — 393.5 kJ/mol, to be precise. The carbon, which may have spent millions of years locked in coal or oil, returns to the atmosphere as CO₂ in a fraction of a second.

We have been burning carbon since we first controlled fire, roughly 1.5 million years ago. The combustion of wood, then coal, then oil, then gas — each transition unlocking more energy per kilogram, and each releasing more stored carbon per century.

The atmosphere now contains 421 parts per million of CO₂. Before industrialization, it held 280.

The fire continues.

CYCLE

Carbon does not disappear. It moves. From atmosphere to ocean, from ocean to plankton, from plankton to sediment, from sediment to stone, from stone to magma, from magma back to atmosphere. The carbon cycle is not a circle but a web — multiple overlapping loops operating on timescales from seconds (photosynthesis) to hundreds of millions of years (tectonic subduction).

Every carbon atom in your body has been something else. It has been atmospheric CO₂, dissolved bicarbonate in seawater, calcium carbonate in a shell, limestone in a cliff, organic matter in soil, glucose in a plant, and — if the atom is old enough — diamond in the mantle, graphite in a metamorphic rock, or methane in the atmosphere of the early Earth.

tanso.bar

Element 6. Atomic weight 12.011.