Magnesium carbonate

Magnesium carbonate is an inorganic salt of magnesium, sold as a soft, white, very light powder. The "gym chalk" you see in weightlifting and climbing gyms is magnesium carbonate, not the calcium-based chalk used on blackboards.

• Formula: MgCO3 (gym chalk is often a basic, hydrated form of it)
• CAS number: 546-93-0 (anhydrous)
• Molar mass: about 84.3 g/mol
• Solubility: practically insoluble in water
• Heat: breaks down at about 350 °C into magnesium oxide and carbon dioxide

It soaks up sweat and oil from the skin's surface, which is why it improves grip. It also fizzes in acids like vinegar, releasing carbon dioxide.

Azlok lists magnesium carbonate as gym chalk powder. The product names don't state a purity grade, so treat it as a technical, general-purpose powder meant for grip and workshop use, not for food, medicine or lab analysis.

See today's price per kg to compare packs.

Most people buy it for grip, but it has industrial uses too.

• Sports grip: weightlifting, powerlifting, CrossFit, rock climbing, bouldering, gymnastics, pole fitness and rope climbing.
• Fillers: a white filler and extender in rubber, paper, paints and some plastics.
• Making magnesium oxide: heating (calcining) it gives magnesium oxide, used in refractories and insulation.
• School and lab demos: showing a carbonate reacting with acid to give carbon dioxide, or thermal decomposition.
• Craft work: a drying, matting powder for some hobby finishes.

Food and pharmaceutical uses need certified grades. This gym chalk listing isn't one of them.

For grip, less is more. A thin, even coat works better than a thick cake on your palms.

1. Fill a chalk bag or bucket: pour in a few spoons at a time. Don't tip the whole 400 g pack into an open bowl, because it floats around and gets everywhere.
2. Chalk up: dip your hands, rub palms and fingers together, then clap once lightly to knock off the extra.
3. Re-chalk between sets, not between every rep. Wipe the bar or hold with a dry brush when caked chalk builds up.
4. Chalk ball: fill an old cotton sock or a refillable chalk ball about two-thirds full and tie it off. It cuts dust a lot, and many gyms ask for this.
5. Liquid chalk (DIY): some climbers mix the powder with rubbing alcohol (isopropyl alcohol) into a thick paste and spread it on the hands. The alcohol evaporates in a minute and leaves a dry coat. It's flammable, so keep it away from flames.
6. After training: wash hands with soap and water and use a basic moisturiser if your skin gets very dry.

Magnesium carbonate is low hazard, but it's a fine dust.

• Avoid breathing the dust. In closed rooms, use a chalk ball, and if you're decanting large amounts, wear a dust mask.
• Keep it out of your eyes. If it gets in, rinse with plenty of clean water.
• Don't use it on cuts, broken skin or rashes.
• Keep it away from acids, which make it fizz and release carbon dioxide.
• Store in a closed container or zip bag in a dry place. It absorbs moisture and clumps when left open.
• Keep it away from children and away from food. Don't eat it or add it to food or drinks.
• Small spills: sweep or vacuum dry. Washing a lot of it down the drain can leave a white sludge.

Choose by how often you train.

• 100 g: enough for a beginner, a gym bag top-up or a few weeks of climbing. Good for testing whether you like loose chalk.
• 400 g: for daily lifters, climbing groups or anyone refilling a bucket. It works out cheaper per kg and lasts months for one person.
• Gyms, academies and resellers: if you need 25 kg or more, send a bulk inquiry for a quote.

If you need magnesium carbonate for food, medicine or analysis, you need a grade with the right certificate, so don't use the gym chalk listing for that.