One hundred and five chemical analyses of augite were used to calculate an average end-members composition (mol.%). The end-members composition consists of: CaMg(Si₂O₆) - 64%, FeFe(Si₂O₆) - 19%, with A1^[IV] - 10%, others - 7%. Some ferroaugite have two dominant end-members CaMgSi₂O₆ (39 mol.%) and CaFeSi₂O₆ (29 mol.%). An average subcalcic augite consists of FeMg(Si₂O₆) (47 mol.%) and CaMgSi₂O₆ (29 mol.%). Titanium has a charge of 4 + in all augites. A maximum CaFe³⁺ AlSiO₆ content (average 22 mol.%) is typical for ferrian augite, but the major end-member is CaMgSi₂O₆ (63 mol.%). During chemical evolution of augite in the Skaergaard intrusion Fe²⁺ initially fills both the M(1) and M(2) positions, and later Fe²⁺ preferentially fills the M(1) position. For pigeonite, Fe²⁺ tends to occupy progressively the M(2) site.