Boron

boron

kernite

borax

colemanite

Formula: B
Element, metalloid, does not occur in the native state on Earth, although it has been identified from the moon
Specific gravity: 2.34
Colour: Black
Solubility: Insoluble in nitric and hydrochloric acids
Melting point: 2075^oC
Boiling point: 3727^oC
Abundance in the Earth’s crust: 10 parts per million by mass, 1 part per million by moles
Abundance in the Solar System: 2 parts per billion by mass, 0.2 parts per billion by moles
Boron compounds are usually found in sediments and sedimentary rock formations. The chief sources of boron are kernite, borax and colemanite. In compounds boron almost always occurs as trivalent B³⁺ (ChC)

Boron-bearing minerals include:

Borides - borides are usually covalent rather than ionic
Chlorides - the chloride anion is Cl^-
Fluorides - the fluoride anion is F^-
Oxides - the oxide anion is O^2-
Monoborates - with a single boron triangle (BO₃)^3- and/or tetrahedron B(O,OH)₄
Diborates - with two boron triangles or tetrahedra or both
Triborates - with three boron triangles or tetrahedra or both
Tetraborates - with four boron triangles or tetrahedra or both
Pentaborates - with five boron triangles or tetrahedra or both
Hexaborates - with six boron triangles or tetrahedra or both
Heptaborates - with seven boron triangles or tetrahedra or both
Nonaborates - with nine boron triangles or tetrahedra or both
Megaborates - with multiple boron triangles or tetrahedra or both
Sulphates - the sulphate anion is (SO₄)^2-
Phosphates - the phosphate anion is (P⁵⁺O₄)^3-
Nesosilicates - insular (Si⁴⁺O₄)^4- groups
Sorosilicate - (Si⁴⁺₂O₇)^6- groups
Cyclosilicates - (Si⁴⁺_nO_3n)^2n- groups
Inosilicates - single chain - (Si⁴⁺_nO_3n)^2n- groups
Phyllosilicates - (Si⁴⁺₂O₅)^2- groups
Tectosilicate - [Al³⁺_xSi⁴⁺O_yO_(2x+2y)]^x−

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