Boracite (Mg3B7O13Cl) containing 19% Boron is an easy choice for my Boron APEX mineral. The few more concentrated minerals are not common and are mostly Hydrates which I am avoiding.
Boron is the last of our low-abundance element trio (Lithium, Beryllium, Boron). However, it does become concentrated on Earth by the water-solubility of its more common naturally occurring compounds (borax and kernite). Boron is a relatively rare element in the Earth's crust, representing only 0.001%. There are commercial borate deposits in Turkey and the United States.
Boron is the first element which exhibits Allotropy. This means the 100% pure element can exist in different forms which display completely different properties. Amphorous Boron is a brown powder and Crystalline Boron is black.Boron compounds were known thousands of years ago. Borax glazes were used in China from AD300,
Boron minerals have been used for thousands of years and are essential to industry. The major industrial-scale uses of boron compounds are in bleaches and insulations. It is also used as an insecticide because it is toxic to bacteria and insects (Roach Powder).
Boron is essential to life. Small amounts of boron compounds play a strengthening role in the cell walls of all plants, making boron necessary in soils. Experiments indicate a role for boron as an ultratrace element in animals, but its role in animal physiology is unknown.