In a small bowl, combine the magnesium chloride flakes and HOT distilled water. Stir until the flakes are completely dissolved, creating a magnesium brine. Set this aside to cool to room temperature.
Make the Lotion
Using a double boiler or a heatproof bowl set over a pot of simmering water, melt the Nature Packaged cocoa butter, beeswax, and avocado oil together. Stir occasionally until fully melted and combined.
Once the oil mixture is melted, remove it from heat and let it cool slightly, but not too much, as it should still be in a liquid state. Slowly add the magnesium brine to the oil mixture, whisking continuously to ensure proper emulsification.
Using a hand mixer or a whisk, blend the mixture until it reaches a creamy, lotion-like consistency. This might take a few minutes. If desired, add a few drops of your chosen essential oils during this step.
Transfer the finished lotion into a clean glass jar. Allow it to cool completely before sealing. Store your magnesium lotion in a cool, dry place. It should last for several months.