Minerals & forms
Magnesium citrate vs oxide: which is in your electrolytes?
The same milligram number on two labels can come from very different ingredients. Here is the simple chemistry, and why it shows up in your glass.
Short answer. Magnesium oxide is dense and cheap: about 60% of its weight is magnesium, but it barely dissolves in water. Magnesium citrate is bulkier, at about 16% magnesium, and it dissolves easily. In a drink, that is the difference you can see and taste. Rawstone uses magnesium citrate, 75mg per serve.
Magnesium turns up on the label of most electrolyte powders and supplement tubs. What almost nobody explains is that "magnesium" on a label is never just magnesium. It is always joined to a partner, and that partner changes a lot. It changes how much powder it takes to hit the number on the label. It changes whether the powder dissolves. And in a drink, it changes what you see and taste. The two forms you will meet most often are magnesium oxide and magnesium citrate. Here is the simple chemistry.
What a magnesium "form" is
Pure magnesium is a reactive metal, so it is never sold as a loose powder in food. It is bonded to another compound to make something stable you can scoop. That partner is the "form".
- Magnesium oxide is magnesium joined to oxygen. It is a plain white mineral powder.
- Magnesium citrate is magnesium joined to citrate, which comes from citric acid, the sour compound in lemons and limes.
You will also see forms like glycinate, mostly in capsules. Each partner is a different trade-off in weight, taste and cost.
The simple maths: how much magnesium is in each
Every atom has a weight. A magnesium atom weighs about 24.3 units, an oxygen atom about 16. So in magnesium oxide, the magnesium share is easy to work out:
Magnesium citrate (the common trimagnesium form, without water): three magnesium atoms weigh about 72.9, in a molecule that weighs about 451. So 72.9 ÷ 451 ≈ 16% magnesium by weight.
Now turn that into a scoop. To put 75mg of magnesium on a label, you need roughly 125mg of magnesium oxide, or roughly 465mg of magnesium citrate. Citrate takes almost four times as much powder for the same number. That is why oxide is so popular: it is dense, it is cheap, and it makes a big label number easy to hit.
Will it dissolve? The glass-of-water test
This is where the two forms really part ways. Magnesium oxide barely dissolves in water. Stir it into a glass and much of it hangs around as a cloudy haze, then settles as grit. Magnesium citrate dissolves easily and disappears into the drink.
This is not just kitchen-bench folklore. Researchers at UT Southwestern measured it directly (Lindberg and colleagues, Journal of the American College of Nutrition, 1990). In plain water, magnesium oxide was close to insoluble, while magnesium citrate dissolved readily.
Why it matters in a drink: taste and mix
In a tablet, solubility is less obvious, because you swallow it whole. In a drink you notice straight away. A form that will not dissolve leaves a chalky film, a gritty last mouthful and a cloudy glass. A form that dissolves gives you an even, clean drink from the first sip to the last.
Taste matters too. The citrate part is gently tart, so it sits comfortably with fruit flavours instead of fighting them. That is a big reason citrate suits a powdered drink so well. The trade-off is cost and bulk: citrate costs more, and it takes up more of the scoop.
How much magnesium makes sense?
More is not automatically better. Australia's Nutrient Reference Values, set by the NHMRC, give adults an upper level of 350mg a day of magnesium from supplements. That limit is for supplemental magnesium only, on top of what you get from food. It is a useful yardstick when you add up the tubs and capsules in your cupboard.
Where Rawstone sits
Rawstone uses magnesium citrate, 75mg per serve. It sits alongside 1000mg of sodium and 250mg of potassium, also as a citrate, with zero sugar and a clean Reb M sweetness. The result is a full-strength hydration powder that mixes clear into a big glass of water and tastes like a drink, not a chemistry set. If you want to see how the sodium dose is set, read is 1000mg of sodium too much, or start with the science of salt and hydration.
Rawstone is launching on Amazon Australia this summer
Sugar-free, magnesium as citrate, and a test certificate will be published from our first batch. Join the list for a launch-day discount code.
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This article is general education about minerals and food chemistry, not medical advice. Rawstone is a food supplement, not a medicine, and is not intended to diagnose, treat, cure or prevent any disease. If you have a kidney condition or take medication that affects your magnesium levels, talk to your doctor before using any electrolyte or magnesium supplement.