When an element reacts chemically with another element to form a chemical compound, it loses or gains one or more electrons in its outer shell, which leaves it with a negative charge (if it gains electrons) or a positive charge (if it loses electrons).
One element may substitute for another in a mineral crystal lattice when its atoms are of a similar size and charge.
A dike cuts upward through layers of rock and so is relatively perpendicular to the layers; a sill intrudes between sedimentary layers and so is relatively parallel to the layers.
Flood basalts form when the lava simply flows out onto the surface through cracks or fissures and spreads widely over large areas.
Most sediments that form from weathering consist of silicate minerals because silicates are the most abundant group of minerals in Earth's crust and mantle. Many silicate grains survive weathering and become sediments.
Quartz is much more resistant to weathering than the feldspar that weathers to clay particles.
Sand undergoes more cementation when it lithifies to sandstone. Cementation is much less extensive in the lithification of clay because clay sediments undergo a great deal of compaction after burial and are therefore relatively impermeable to mineral-bearing solutions.
Evaporites weather quickly because they dissolve readily.
Graded beds form when a strong current suddenly introduces a large volume of sediment to a quieter body of water. The coarser sediment settles more rapidly than the finer sediment, producing a bed with diminishing grain size from bottom to top. (2) Ripples form when wind or water move over the surface of a sediment deposit. (3) Cross-bedding occurs when sets of parallel beds slope at an angle to the horizontal; the average direction of slope indicates the general direction of the prevailing winds or currents that formed the beds. (4) Mudcracks form when fine-grained, clay-rich sediments dry out and shrink.
Metamorphism alters preexisting rocks without melting them; igneous rocks form by the cooling of rock that has become hot enough to melt.
