Texture In Igneous Rocks The two most obvious textural features of an igneous rock are the size of its mineral grains and how the mineral grains are packed together. Sizes of mineral grains Intrusive rocks are coarse-grained Magma that solidifies in the crust cools slowly and has sufficient time to form large mineral grainsTexture In Igneous Rocks The two most obvious textural features of an igneous rock are the size of its mineral grains and how the mineral grains are packed together. Sizes of mineral grains: ◼ Intrusive rocks are coarse-grained. ◼ Magma that solidifies in the crust cools slowly and has sufficient time to form large mineral grains