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How it works

Crushed rock, rain, and the carbon that stays out of the air.

Enhanced rock weathering in five questions. The short version of what happens on a field — the method in full is on the Science page.

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01 — What is it?

A natural process, sped up.

When rain falls on silicate rock, it slowly dissolves it — and in doing so turns carbon dioxide from the air into bicarbonate, a dissolved form of carbon that stays out of the atmosphere for tens of thousands of years.

On its own this takes geological time. Enhanced rock weathering speeds it up: crush the rock so there is far more surface for water to reach, and spread it on farmland, where rain, soil acids and roots are already working. The chemistry does not change. Only the rate does.

02 — What goes on the field?

Crushed basalt, checked before it leaves the quarry.

Basalt is a common volcanic rock, rich in the calcium and magnesium the reaction needs. India has a great deal of it, often close to farmland — which matters, because hauling rock costs energy and that energy counts against the carbon removed.

Every lot is tested for its composition and for trace metals before it is approved. Lots outside the limits are not used. It is spread at agronomic rates, with ordinary farm equipment, in a window the farmer's season already has.

How basalt is qualified

An open palm holding crushed dark-grey basalt over a steel sieve: angular grains from fine dust to pieces several millimetres across, dust on the fingers, and a centimetre ruler laid across the sieve for scale.
MaterialCrushed basalt prepared for field application.

03 — What happens in the soil, and to the carbon?

From a quarry to the ocean, in five stages.

The carbon ends up somewhere specific. That is what makes the removal durable — and what makes it possible to measure.

  1. 01Rock

    Crushed basalt

    Silicate rock from quarries near the districts we work in, assayed for composition and trace metals before it leaves.

  2. 02Field

    Applied to compatible soil

    Spread at agronomic rates, in a window that already exists in the cropping calendar.

  3. 03Soil

    Rain starts the reaction

    Rainwater carrying dissolved CO₂ forms a weak carbonic acid. It dissolves the rock grains and releases calcium and magnesium.

  4. 04Water

    Carbon becomes bicarbonate

    The reaction converts CO₂ into dissolved bicarbonate — no longer a gas, no longer in the atmosphere.

  5. 05River → ocean

    Carried to the sea

    Bicarbonate drains through soil water and rivers to the ocean, where it is stable for tens of thousands of years.

The reaction, simplified for a calcium silicate

CaSiO3 + 2CO2 + H2OyieldsCa2+ + 2HCO3− + SiO2

Results vary with

  • Rock chemistry
  • Particle size
  • Application rate
  • Soil chemistry
  • Rainfall and hydrology
  • Baseline conditions
  • Haulage distance
  • Measurement design

Not all of it arrives. Strong acids from nitrogen fertiliser can dissolve rock without capturing CO₂, and some carbon can re-precipitate in the soil. Those losses have to be accounted for, not assumed away. Why soil type changes the answer

04 — How is it measured?

Sampled before, sampled after, compared.

A field is sampled before any rock touches it, then resampled across seasons. Removal is calculated from that record, net of every operation's emissions, with its uncertainty stated. The full measurement method

A field technician in a hat and work gloves driving a hand soil auger into bare soil between rows of young maize. Beside him, a marker stake, an orange flag, two labelled soil sample bags, a handheld GPS unit, a measuring tape, a brush and a notebook; sample labels are obscured.
BaselineSoil sampling before any basalt is applied.

  1. Select compatible land

    Soil class, rainfall, cropping calendar and haul distance decide whether a field is a candidate at all.

    Zone model

  2. Characterise the field

    Plot boundaries are recorded, and baseline soil is sampled at depth before anything is applied.

    0–15 · 15–30 cm

  3. Source and qualify basalt

    Every lot is assayed for composition and trace metals. Lots outside threshold are not used.

    XRF · Ni Cr V

  4. Apply the rock

    Spread at agronomic rates, with the equipment and in the season the farmer already works to.

    Custody chained

  5. Sample and monitor

    The same plots are resampled across seasons and compared with their own baseline.

    Georeferenced

  6. Analyse

    Every sample runs one panel: total elemental, exchange chemistry, conversion basis and safety metals.

    One sample, two uses

  7. Quantify removal

    Removal is calculated net of quarrying, grinding, haulage and spreading, with uncertainty carried through.

    Net · with interval

Field sites

Site record — template

No field site is published yet

Each site will appear here once its details are confirmed, with every field below filled in and a status that says only what has actually happened.

Location
Published when confirmed
Soil context
Published when confirmed
Crop
Published when confirmed
Rock source
Published when confirmed
Application
Published when confirmed
Sampling
Published when confirmed
Measurement
Published when confirmed
Current status
Published when confirmed

Statuses used: Research · Field trial · Active deployment · Monitoring · Data analysis · Verified

Going further

The method in full, including the parts that are hard.

Geochemistry, the five soil zones, sampling design, uncertainty and the published work the method is built against.

Explore the scienceWork with Bhu Carbon