Magma Molten rock beneath the surface of the Earth. When magma spills onto the surface of the Earth (maybe from a volcano) it is called lava.
Magnetic stripes Tectonic plates move around the Earth. It is believed that the ocean floos are spreading so that the continents are moving further apart. Measurements of magnetic properties along the ocean floor show that the rock has been formed at different times.
Mantle The layer of the Earth immediately below the crust. Beneath the mantle is the core.
Melting point The temperature at whcih a solid turns into a liquid.
Metal A metal is a substance whose atoms are so close together that their outer shells overlap. This allows electrons to wander from atom to atom as part of a delocalised sea of electrons. This allows the metal to conduct electricity. Metals also conduct heat, are shiny, malleable and ductile, sonorous. They also (usually) have hig melting points and boiling points.
Metamorphic Referring to rock types it means that the rock has been changed by the action of heat and / or pressure. Examples include marble (which is formed from limestone).
Minerals The chemical substances from which rocks are made.
Mixture Two or more substances loosely joined together. The substances are not chmically joined together. Mixtures can usually be separated into their components quite easily.
Molecule Two or more atoms joined together by a covalent bond. Molecules can be elements (eg H2 , O2 etc) or compounds (eg CH4 , H2SO4).
Molecular formula This shows the number of each kind of atom in a molecule. (eg CH4 has one carbon atom and four hydrogen atoms; H2SO4 has two hydrogen atoms per molecule, one sulfur atom and four oxygen atoms per molecule)
Mortar It is made by mixing sand and cement with water. It sets hard and is used to hold bricks etc together.
Mudstone A sedimentary rock made from small particles of mud.
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