Igneous rocks formed from lava flows of the Archaean era (>2,700 million years ago) are often found to contain disequilibrium-textured crystals characterized by spherulitic, branching or dendritic morphologies that occur in layers near the flow surface.
Crinoid fossils. Rock containing crinoid (or sea lily) fossils. These are Scyphocrinus elegans crinoids from the Silurian/Devonian period (about 440-360 million years ago). Crinoids are marine echinoderms that appear as early as the Ordovician period (500 million years ago).