Mohs Index                               Rock Can be scratched by

1 (softest) Talc

2 Gypsum                                     Fingernail

3 Calcite                                       Copper coin

4 Fluorite

5 Apatite                                       Pocket knife

6 Orthoclase                             Steel file

7 Quartz

8 Topaz

9 Corundum

10 (hardest) Diamond 

Basalt: A dark-colored, extrusive igneous rock.

Bedrock: A fixed rock formation, which may be exposed to view or covered by soil, vegetation, or sediments.

Breccia: A sedimentary rock made up of large angular fragments.

Crystal: A solid substance that has a well-defined internal order and a characteristic shape.

Dolostone: A type of sedimentary rock consisting chiefly of dolomite (magnesium carbonate). It is usually formed by chemical precipitation.

Extrusive rock: A type of igneous rock that forms from magma after it has erupted onto the surface of the earth.

Field guide: A picture book, easily carried on trips, that helps identify minerals, rocks, fossils, or other objects or creatures.

Foliation: The layer like alignment of crystals in metamorphic rocks.

Gneiss: A metamorphic rock that shows foliation in the form of bands of light and dark crystals.

Halides: One of the mineral chemical groups containing halogen. Ex: rock salt, fluorite. Igneous rock: Rock formed by magma cooling to solid state.

Igneous:  «IHG nee uhs», rock is rock formed by the hardening and crystallization of molten material that originates deep within the earth.

Intrusive rock: A type of igneous rock formed by magma that solidifies underground.

Magma: Molten rock beneath the earth’s surface.

Metamorphic rock: Rock that is formed when sedimentary or igneous rocks are altered (but not completely melted) by geologic forces.

Mineral: A naturally occurring, nonliving, crystal- forming substance.

Oxides: One of the mineral chemical groups containing oxygen. Ex: bauxite, cuprite, and magnetite.

Phosphates: One of the mineral chemical groups. Ex: apatite and turquoise.

Quartzite: Metamorphosed sandstone.

Schist: A type of common metamorphic rock that shows foliation.

Sedimentary rock: Rock formed by the accumulation of rock particles or the remains of animals or plants, or by chemical precipitation.

Shale: A type of sedimentary rock, formed by the accumulation of clay particles.

Silicates: One of the mineral chemical groups. Ex: mica, feldspars, quartz, talc, and garnet.

Streak Plate: A piece of unglazed porcelain used to determine the color of mineral streaks.

Sulfates: One of the mineral chemical groups. Ex: gypsum and barite.

Sulfides: One of the mineral chemical groups containing sulphur. Ex: cinnabar, pyrite, and galena.

Ammonite: A type of extinct cephalopod mollusk that had a shell marked with sutures. Especially common in the seas of the Mesozoic Era.

Arthropod: A member of a large group on invertebrate animals which includes trilobites, crabs, insects.

Brachiopod: An invertebrate sea animal that has two valves that are not close copies of one another.

Carbonization: The type of fossilization that occurs when an organism’s tissue is reduced to a thin layer of carbon. Many plant fossils are preserved it this way.

Cast: A fossil in which the original organism has been dissolved away and replaced with rock material. It often resembles the structure of original organism.

Cephalopod: A type of mollusk that includes forms common in the fossil record. Ex: ammonites and squids.

Concretion: A round or oblong stone nodule that often contains a fossil at its center.

Crinoid: A plantlike sea animal; a type of echinoderm. Also called sea lily.

Echinoderm: A type of invertebrate sea animal. Ex: starfish, sea urchins, crinoids.

Fossil: The remains of a past plant, animal, or other living being, found preserved in the earth’s crust.

Index fossil: A fossil that helps to determine the identity or age of a particular rock unit. Invertebrate: An animal that does not have a backbone. Ex: arthropods, mollusks, brachiopods, echinoderms.

Mold: The impression left in surrounding rock by a shell or other organic structure.

Mollusk: A very widespread type of invertebrate animal common in the fossil record. Ex: Cephalopods and gastropods.

Paleontology: The branch of geology devoted to the study of ancient life-forms, as revealed by fossils.

Paleozoic: the second of four eras of the geologic time scale.

Pelecypod: A type of mollusk that has two valves that usually are close copies of one another. Ex: clams and oysters.

Placoderm: A type of early armored fish that was common in the Devonian Period of the

Paleozoic Era. Suture: A marking, often resembling a complicated wavy line found on an ammonite shell. The suture is the line along which the wall of achamber meets the wall of the outer shell.

Paleozoic Era. Valve: A shell part that helps to enclose the soft tissues of brachiopods, pelecypod, and other invertebrates. Vertebrate: An animal that has      a backbone. Ex: fish, reptiles, and birds.

Trilobite: An extinct type of arthropod sea animal, very widespread in the fossil record of the