Borates in nature
Boron is one of the 118 known chemical elements, atomic number 5 on the periodic table. It exists naturally in soil, water, plants and animals. In fact, boron is one of seven essential micronutrients that plants need to grow. Working on the cellular level, boron is central to a plant's reproductive cycle, controlling flowering, pollen production, germination, and seed and fruit development. The mineral also acts as a fuel pump, aiding the transmission of sugars from older leaves to new growth areas and root systems.
On a global basis, boron moves naturally through the atmosphere at a rate of five to seven million tons per year. The element boron does not exist by itself in nature; it occurs in combination with oxygen and other elements in compounds called borates. Common borate compounds include borax, boric acid and boric oxide.
Rio Tinto Minerals' primary borate deposit
While boron is common in the world around us, borate deposits large enough to be commercially mined are exceedingly rare. Rio Tinto Minerals' primary borates deposit in the Mojave Desert was formed about 19-20 million years ago as a basin formed by several active lava flows. Over several thousand years, water collected in the basin, forming a lake. Clay from surrounding rock formed an impermeable layer at the bottom of the lake. Natural hot springs rich in boron then flowed in the lake, quickly cooling to form borate crystals. Another layer of clay then washed in, effectively sandwiching the rich borate deposits.
About 19 million years ago, the lake dried up, leaving borate crystals embedded in the clay. Over time, the clay was covered by layers of sand, burying the deposit more than 2,000 feet underground. Tectonic movement, combined with years of erosion, eventually forced the borate deposit upwards, to within 150 feet of the surface.
More than 80 types of minerals have been found in our mine, including the four most common forms of borate ore:
The most abundant ore in the deposit, tincal was used by ancient Romans to make glass.
The second most abundant ore, named after Kern County, California, where the mine is located. Crystals of Kernite more than five feet long have been found in the mine.
This form of ore takes on many different shapes. It can look like a mushroom, a cauliflower, a snowball or cotton ball. In fact, "cotton ball" is a common nickname for this mineral.
Colemanite gets its name from one of Borax's founding fathers, William T. Coleman.