Boron (B), named after the mineral borax, from which it was isolated, is a dark metal with similar properties to carbon in elemental form. Pure boron is nearly as hard as diamond, but is not naturally occurring on Earth.

Boron can be isolated from boric acid, which is used in some bug killers in a white powder form. Using a ceramic plate that you don’t mind parting with (i.e. the plate under a flower pot), heat up boric acid to boil off excess water. It will turn an off-coloured white before eventually transforming into a thick glassy paste, boron dioxide. Once it stops letting off steam, usually about 30 minutes in, allow it to cool.

Break the cooled glass into a fine powder and mix 1:1 with magnesium powder. Use a little bit more magnesium to ensure all of the boron dioxide burns. Ignite this mixture with a fuse or sparkler to create a thermite reaction. As soon as the reaction stops, cover it to prevent the boron from oxidising.

Put the reactant in a glass beaker and cover with water. Slowly add
hydrochloric acid to separate the magnesium and boron. This reaction will produce flammable chlorine gas.

After the solution stops reacting, pour it through a coffee filter to separate the liquids and solids. The remaining black solids are elemental boron.

There is a video demonstrating this process on YouTube.