Earth’s Crust, Minerals, Rocks, and Elements
Earth’s Crust
The crust is the outermost layer of the Earth. Principal relief features include:
- Continental Shelf: Prolongation of the continent under the ocean.
- Abyssal Plain: Flat surface located about 6,000-12,000 meters deep, forming most of the ocean floor.
- Continental Slope: Slope between the continental shelf and the deep sea-bottom.
- Ocean Trenches: Deep depressions over 10,000 meters, associated with edges of continents and archipelagos.
- Seamounts: Underwater mountains.
- Oceanic Ridges: Large mountain ranges that cross the sea bottom.
Main Geochemical Features
Key elements found in the crust include:
- Silicon: Combined with oxygen and other elements to form different compounds, primarily silicates. Silicon combined with oxygen forms silica (quartz), which is used to manufacture microchips and is good for bones.
- Aluminum: Usually combined with silicon to form aluminum silicates, used in cars, planes, soda cans, etc. In high doses, it can cause health problems.
- Iron: Is strong and magnetic. Iron oxide (iron combined with oxygen) is used to make steel.
- Magnesium: Used in the construction of spacecraft. With air jets, it produces white light.
- Calcium: Calcium oxide is lime. Calcium is part of the bones of vertebrates. Milk and dairy are the most calcium-containing foods.
Minerals
Minerals are naturally occurring solid substances with a defined chemical composition and crystal structure. Their physical properties include:
- Density: The ratio of a body’s mass to its volume.
- Color: In some minerals, the color is constant and characteristic; however, others may have different colors due to impurities, or this property may not be useful for identification.
- Hardness: The resistance a mineral has to being scratched.
- Luster: The appearance of a mineral surface as it reflects light. It can be metallic or non-metallic.
- Cleavage: The tendency of a mineral to break along flat surfaces.
Classification
Minerals are classified based on their chemical composition:
- Silicate Minerals: Formed by silicon and oxygen, and often contain other chemical elements such as iron, calcium, magnesium, etc. The most common are quartz and mica.
- Non-Silicate Minerals: As their name indicates, they are not formed by silicon but by other elements. These include:
- Native Elements: Pure substances formed by a single element (e.g., gold, silver).
- Oxides: Formed by oxygen and other elements (e.g., iron oxide, magnetite).
- Sulfates: Formed by sulfur and oxygen (e.g., gypsum).
- Sulfides: Formed by sulfur and other elements (e.g., pyrite).
- Carbonates: Formed by carbon and oxygen (e.g., calcite).
- Halides: Formed by a halogen element (like chlorine or fluorine) and another element. Many have a salty taste (e.g., halite (table salt), sylvite, carnallite).
Rocks
Rocks are naturally occurring solid aggregates of one or more minerals or mineraloids. They are classified into three main types based on their formation:
- Igneous or Magmatic Rocks: Formed from the cooling and solidification of magma (molten rock). When magma cools slowly underground, it forms plutonic rocks (e.g., granite). When lava cools quickly on the surface, it forms volcanic rocks (e.g., basalt).
- Metamorphic Rocks: Formed from other rocks that have been subjected to high pressure and temperature, causing them to change their mineral composition or texture.
- Sedimentary Rocks: Formed by the accumulation and cementation of sediments. Groups include:
- Detrital Sediments: Formed by the accumulation of rock fragments (e.g., conglomerates, sandstones, argillite).
- Chemical Precipitation: Occur when minerals dissolved in water form crystals (e.g., halite, lime, gypsum).
- Organic Origin: Formed by the accumulation of organic remains (e.g., coal, oil).
Elements and Substances
Selected Elements
A list of some elements from the periodic table:
- Hydrogen H
- Helium He
- Lithium Li
- Beryllium Be
- Boron B
- Carbon C
- Nitrogen N
- Oxygen O
- Fluorine F
- Neon Ne
- Sodium Na
- Magnesium Mg
- Aluminum Al
- Silicon Si
- Phosphorus P
- Sulfur S
- Chlorine Cl
- Argon Ar
- Potassium K
- Calcium Ca
- Gallium Ga
- Germanium Ge
- Arsenic As
- Selenium Se
- Bromine Br
- Krypton Kr
- Rubidium Rb
- Strontium Sr
- Indium In
- Tin Sn
- Antimony Sb
- Tellurium Te
- Iodine I
- Xenon Xe
- Cesium Cs
- Barium Ba
- Thallium Tl
- Lead Pb
- Bismuth Bi
- Polonium Po
- Astatine At
- Radon Rn
- Francium Fr
- Radium Ra
Pure and Mixed Substances
- Pure Substances: Consist of a single component (e.g., an element or a compound).
- Mixtures: Consist of two or more substances that are physically combined and can be separated by physical means.
- Homogeneous Mixture: Appears uniform throughout, resembling a pure substance, but consists of multiple components (e.g., saltwater).
- Heterogeneous Mixture: The presence of several components can be distinguished visually or with a microscope (e.g., sand and water).