Sign up for news of special offers, new products and fossil hunt dates

Glossary

A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|V|U|W|X|Y|Z

Abbess	The position of an Abbess in her convent corresponds to that of an Abbot in his monastery.
Acidic rock	A type of igneous rock consisting mainly of lighter colour minerals such as quartz and feldspar. It is dominated by silica. It has fewer darker coloured minerals such as mica and hornblende. Example: granite or rhyolite lava.
Alkaline rock	A type of igneous rock that is made up of less than half by silica. It is normally dominated by dark-coloured minerals such as hornblende and pyroxenes. Example: basalt and gabbro.
Amber	Fossilised resin from trees. Often contains very well preserved insects.
Ammonite	Extinct mollusc group known as cephalopods.
Arthropod	An animal with jointed legs, a segmented body and an exoskeleton. e.g trilobite.
Asthenosphere	The weak part of the upper mantle just below the lithosphere, in which slow convection is thought to take place.
Atom	The smallest particle of an element that possesses all of the properties of that element.

Basalt	An igneous rock which forms from hardened lava after a volcanic eruption.
Basic rock	An igneous rock with a silica content of less than two thirds. It contains a high proportion of dark-coloured minerals.
Batholith	A very large body of plutonic rock that was intruded deep in the Earth's crust.
Belemnite	An extinct type of cephalopod that was related to the modern-day squid.
Biotite	A dark-coloured form of the mineral mica associated with basic rocks.
Black Smoker	Deep sea hot water vents. They are associated with volcanic activity and are found on the sea floor at mid ocean ridges. Mineral-rich water is pumped out at high temperatures (about 350 degrees celcius). When the hot mineral rich water meets the cold sea water, it releases the minerals leaving large deposits on the sea floor. In time, the minerals build up around the vent to produce tall chimney stacks. Black smokers were first found in 1977.

Calcite	A mineral that is composed of calcium carbonate.
Cambrian	Cambrian Period. The first period of geological time in the Palaeozoic Era, beginning 550 million years ago and ending 495 million years ago.
Carbonate	A chemical compound containing ion groups made up of one carbon atom combined with three oxygen atoms. Examples: calcium carbonate, potassium carbonate, sodium carbonate.
Carboniferous	Carboniferous Period. A period of geological time between 354 and 290 million years ago. It was characterised by large coal forming forested swamps.
Cast	A fossil that forms when minerals harden inside a mould.
Cenozoic Era	The most recent era of geological time that began 65 million years ago at the end of the Mesozoic and continues to the present day.
Chalk	A soft limestone made up of tens of millions of coccoliths, the remains of tiny sea organisms.
Clastic rock	A sedimentary rock that is composed of fragments of pre-existing rocks that have been carried by ice, water or wind and deposited.
Clay	A water derived sediment made of tiny flakes of material that sink to the bottom and build up slowly.
Cleavage	The tendency of some minerals to split easily along planes that are parallel to a crystal face, leaving a smooth surface in one or more directions. Example: mica possesses perfect cleavage in one direction.
Coal	Carbon-rich solid rock that is composed of fossilised plant remains. It is only found in sedimentary rocks that were deposited on the land so when we find coal in rocks it tells us what the earth was like when the coal was deposited.
Contact metamorphism	The changes that take place in rocks when they are in direct contact with hot molten magma. Example: marble.
Continental drift	The theory that the Earth's continents were once one single land mass that moved and split up to form the shape of the continents we see today.
Coprolite	Fossilised animal droppings.
Core	The centre of the Earth. The inner core is solid and the outer core is liquid
Corundum	Better known as the precious gem stones ruby and saphire. Corundum is used to make abraisives such as emery paper.
Cretaceous	The last period of the Mesozoic Era. It lasted from 142 to 65 million years ago. It ended with the extinction of the dinosaurs and ammonites.
Crust	The thin outer rocky layer of the Earth. It varies in thickness between 7 and 70 km. It makes up less than 1% of the Earth's volume.

Crystal	The special shape in which minerals form. A crystal has fixed properties and the sides are usually flat and regular.
Crystalline	A mineral that has been unable to produce well formed crystals. Quartz often forms in this way when an agate geode forms.

Density	The weight of a unit of volume of a body.
Devonian	The geological period that lasted from 417 to 354 million years ago. Its name comes from the fact that rocks of this age are commonly found in Devon. It is known as the age when fish evolved.
Diamond	The hardest mineral on earth. It is four times harder thasn corundum. It is made of just carbon that has been heated and pressurized deep in the Earth. Diamonds are used as precious stones or for drilling and cutting really hard substances like rock.
Dinosaurs	The group of extinct reptiles that lived on the Earth between 230 and 65 million years ago.

Eocene	The geological epoch that lasted from 55 to 43 million years ago. This was the time when mammals became the dominant land vertebrates.
Eon	the largest division of geological time. An eon is divided into eras. there have been three eons. The Precambrian is divided into the Achaean and Proterozoic eons. The Phanerozoic eon includes all the time from the beginning of the Cambrian to the present day.
Element	A material that cannot be broken down into a more simple substance by chemical processes. It is a fundamental chemical building block. example: sulphur or oxygen.
Erosion	The wearing away and transportation of rock by the action of water, ice and wind
Era	A subdivision of a geological Eon in the geological time scale. An era is divided into two divisions called periods.
Evaporite	Sediment rocks formed by the evaporation of seawater in enclosed basins.
Evolution	The way in which organisms change over time.
Exoskeleton	A hard shell that covers soft body parts. Very common in arthropods such as crabs lobsters and trilobites. It is quite common for the creature to shed the exoskeleton at regular intervals. The fossils of trilobites are often made from a shed exoskeleton. A single trilobite could be responsible for producing many fossils.
Extinct	Died out from the Earth forever
Extrusive rock	An igneous volcanic rock that has cooled and hardened on the Earth's surface.

Fault	A break in the Earth's crust along which movement has occurred. It may result in a difference in the position of the rock layers on either side.
Feldspar	The most common silicate mineral on Earth.
Formation	A word used to describe a sequence of related rock layers or beds.
Fossil	Any evidence of past life, including remains, impressions and traces.
Fossil fuel	The remains of ancient plants and animals that we burn to create heat and electricity.

Gabbro	An alkaline igneous plutonic rock. It is the
Geode	A hollow lump of rock that usually contains crystals.
Geological Time Scale	The way that scientists divide time to understand what the Earth was like in the past.
Geology	The study of rocks
Gneiss	A metamorphic rock with large grains that has been formed by the partial melting of existing rocks.
Gypsum	A mineral composed of calcium sulphate

Hardness	Ability of one substances to scratch another. Hardness is used as a way to identify different minerals by applying Mohs' hardness scale.
Herbivore	Vegetarian or grazing animal
Hydrothermal	This refers to water and the action of water that has been heated up by volcanic activity. A hydrothermal vent is an underground geyser.

Igneous Rock	A rock type that has formed through the cooling and solidification of magma. e.g. granite, lava.
Impervious	A rock that will not let water pass through it.
Invertebrate	An animal without a backbone. Example: trilobite, insect.

Jurassic

Jurassic Period, the second period in the Mesozoic Era. It lasted from 205 to 142 million years ago.

Lava	The hot melted rock which pours out of an erupting volcano.
Limestone	A sedimentary rock that is mostly composed of calcium carbonate. e.g. chalk.
Living Fossil	A creature which represents the relics of ancestral stock which have survived long after the parent groups which gave rise to them have vanished
Lustre	The way in which a mineral reflects light. This property is used to identify different minerals.

Mass Extinction	A time when large groups of species on the planet are killed off.
Magma	The hot liquid rock deep in the Earth's crust which becomes lava when it is expelled from a volcano during an eruption.
Mammal	A warm-blooded, hair covered animal that gives birth to live young.
Mantle	The layer between the crust and the outer core. It is made of liquid rock known as magma.
Mass Extinction	A time when the majority of the species living on the Earth were killed off. Example: there was a mass extinction at the end of the Cretaceous which included the extinction of the dinosaurs.
Mesozoic Era	Geological Era that lasted from 248 to 65 million years ago. It is known as the age of the dinosaurs.
Matrix	The rock or sediment in which a fossil is embedded.
Metamorphic rock	A type of rock that forms when heat and pressure changes the minerals in igneous, sedimentary or other metamorphic rocks.
Meteorite	A lump of rock from outer space which has collided with the Earth's surface
Mica	A soft silicate mineral with flat shiny flakes that are found in many rocks such as granite. It has perfect cleavage.
Miocene	The geological epoch of time that lasted from 24 to 5 million years ago.
Mid Ocean ridge	A long chain of under sea mountains where basalt erupts periodically to form new oceanic crust.
Mineral	A specific compound of elements, or a single element which forms crystals. All rocks are made from minerals.
Mohs' Hardness Scale	A relative scale of mineral hardness designed to put minerals into an order. It was invented by the Viennese mineralogist Frederich Mohs. The hardest mineral is diamond with a value of 10 and the softest mineral is talc with a hardness of 1.
Mountain belt	A region where there are many ranges of mountains usually associated with the collision of continental plates.
Mudstone	A fine-grained massive rock that has been formed by the compaction of mud through burial.

Obsidian	A glassy volcanic rock that was produced when lava cooled down very rapidly. It cools so fast that minerals do not get time to grow as crystals. Snowflake obsidian if formed when white quartz crystals begin to appear as spots after the obsidian has been exposed on the Earth's surface.
Oligocene	The geological epoch of time that lasted from 34 to 24 million years ago.
Ordovician Period	The geological period that lasted from 495 to 443 million years ago.
Ore Mineral	A mineral that occurs in sufficient quantity to be mined for its metal content. For example: haematite (iron ore).
Orogeny	A period of mountain building through collision of tectonic plates.

Permian	Permian Period, the last period in the Palaeozoic Era that lasted from 290 to 248 million years ago.
Palaeontology	The study of fossils
Palaeozoic	The geological era that lasted from 545 to 248 million years ago. It is the period when land plants developed and the dominant animals were fish.
Petrification	The process that turns organic material into stone by mineral replacement. If wood becomes buried it can become petrified by quartz.
Piezoelectricity	The property of some minerals to produce an electrical charge when placed under mechanical pressure.
Phanerozoic Eon	The most recent eon, beginning at the start of the Cambrian Period, some 570 million years ago and extends to the present day. It represents the time from when life was first observed on the Earth.
Plankton	tiny animals that live near the top of the water. It is an important source of food for many sea creatures.
Petrified	When the tissues of a dead plant or animal have been replaced by minerals such as silica they are said to be petrified. This often happens to wood.
Petroleum	The carbon-rich, and mostly liquid mixture produced by the burial and partial alteration of animal and plant remains. Liquid petroleum is called oil and the gaseous part is known as natural gas.
Plate Tectonics	The established theory that the Earth's crust and upper mantle, the lithosphere are broken into a number of more or less rigid but constantly moving slabs or plates.
Permian	The last geological period of the Palaeozoic Era. It lasted from 290 to 248 million years ago.
Pleistocene	The geological epoch that lasted from 2 million to 10,000 years ago. It was the time of the last Ice Age.
Plesiosaur	An extinct, long necked marine reptile.
Pliocene	The geological epoch that lasted from 5 to 2 million years ago.
Plutonic	An igneous rock that was formed by slowly cooling magma that solidified deep in the Earth's crust. Plutonic rocks usually possess large mineral crystals. e.g. Granite.
Precambrian	The earliest geological period, which lasted from 4,600 million years ago to 545 million years ago. Life on Earth began to appear towards the end of the Precambrian.
Pterosaur	An extinct flying reptile that lived during the mesozoic.
Pyrite	Iron sulphide. It is common in sedimentary rocks that were deposited in conditions of low oxygen. It sometimes forms fossils casts of ammonites.
Proterozoic Eon	This includes the time from 2.5 billion years to the beginning of the Cambrian Period about 600 million years ago. It represents a time when very little life on Earth has so far been been discovered in the fossil record.
Pyroclastic	Any solid material that has been ejected from a volcano
Pyroclastic flow	Solid material ejected from a volcano, combined with extemely hot gases which together behave as a high-density fluid. Pyroclastic flows can cause extensive damage when they flow down the slopes of a volcano during an eruption.

Quaternary Period

The second period in the Cenozoic Era beginning 1.6 million years ago and continuing to the present day. It is the time we live in.

Radiometric Dating	The method of dating a material by the use of the radioactive elements it contains. The rate of decay of any element changes in a predictable way. This allows a precise date to be given for when a material was formed.
Reptile	A cold-blooded creature that gives birth to young by laying eggs.
Resin	A sticky substance produced by certain plants (conifers). Amber is a fossil resin. Because it is sticky, many insects become trapped in the resin that later becomes amber. Young amber is called copal.
Rock	Naturally occurring solid material containing one or more minerals

Sandstone	A sedimentary rock that is composed of cemented grains of sand
Schist	A metamorphic rock characterised by a shiny surface of mica crystals all oriented in the same direction.
Sediment	Any solid material that has settled out of suspension in a liquid
Sedimentary Rock	A Layered clastic rock formed through the deposition of pieces of mineral, rock, animal or vegetable matter.
Shale	A fine grained sedimentary rock made of clay minerals that has been compacted through burial.
Silica	Silicon dioxide. A very common mineral occurring as quartz, chalcedony, agate, flint, amethyst etc.
Silurian	A geological period that lasted from 443 to 417 million years ago. It was named by a tribe called the Silurs who used to live in Britain.
Siphuncle	A single tube that connects the shell chambers of cephalopods such as ammonites and nautiluses and orthoceras. Cephalopods pumped gas and fluid through this tube to control their depth in the water and to control their orientation in the water.
Slate	A low-grade metamorphic rock that has been produced by pressure through burial. It was originally deposited as claystone but the pressure results in the clay minerals aligning themselves parallel to one another. The direction of the alignment is usually 90 degrees to the direction of the pressure.
Stratigraphy	The study of the history and conditions of formation of the Earth's sedimentary rocks.
Stratification	The formation of layers in rock through deposition of rock particles and compaction.
Streak	The colour of the powder that a mineral produces when rubbed across a piece of unglazed porcelain (the back of a wall tile). The distinctive colour that mineral produces is used to identify mineral types.
Suture	The junction of two or more parts of a skeleton. In cephalopods it the junction of the septum with the inner wall of the shell. It is very complex and distinctive in ammonoids and the pattern is used to identify different species.

Tectonic plate	One of the great slabs of the Earth's lithosphere that covers the surface of the Earth.
Tertiary Period	The first period of the Cenozoic Era. It began about 665 million years ago and ended 1.6 million years ago.
Trace fossil	Ancient evidence of life on Earth. These might be foot prints or trails. Trace fossils tell us a lot about and where a creature lived.
Translucent	The description of a mineral that allows light to penetrate but not pass right through it.
Transparent	The description of a mineral that allows light to penetrate and also pass through it.
Triassic	The first geological period of the Mesozoic Era. It lasted from 248 to 205 million years ago.

Vertebrate	An animal that possesses a backbone. for example Mammals and reptiles.
Vesicle	A small cavity in a volcanic rock that was originally created by a bubble of trapped air in molten lava.
Volcanic	Anything that has been produced from volcanic activity. Volcanic rocks are igneous rocks that have been ejected from a volcano and have cooled on the earth's surface.

Zone Fossil

A fossil from a recognisable species of creature that lived for a relatively short time. Tilobites and ammonites make good zone fossils because it is quite easy to recognise different types by their shape.
Zone fossils help palaeontologists to date rocks.