Diabase /ˈdʌɪəbeɪs/ – a rock that has a holocrystalline fine-grained structure. Diabase is chemically similar to basalt, which equalizes some of their characteristics. A distinctive feature of diabase is its fairly minimal concentration of silica, which is equal to 40-50%.
Ex. High-denisity basalt and diabase aggregate is used in the concrete shields of nuclear reactors.