ABOUT MINERALS ROCKS, AND DECORATIVE STONES

On this page: What are minerals? What are gemstones? What are rocks? Looking after a mineral collection Recommended books Recommended museums

Bright red crystals of vanadinite from Morocco

What are minerals?

Where are minerals found?

Minerals are formed in many different geological environments but most of them are conveniently found as concentrations in mineral veins or ‘lodes’ as a result of the influence of heat and pressure deep underground. Hot solutions have dissolved rocks, liberating chemical elements and allowing them to recombine as new mineral species elsewhere, usually in cavities and fissures. The resulting mineral veins and lodes often contain metalliferous minerals of economic value, the exploitation of which has provided the majority of mineral specimens in Britain’s museums. 
 
The main orefields in Britain producing mineral specimens were in Cornwall and Devon, Wales, Derbyshire, the Northern Pennines, the Lake District and the Southern Uplands of Scotland. The east and south-east of England, with its cover of soft, relatively young sedimentary rocks, unaffected by volcanism or tectonic disturbance, have yielded few minerals but there are some, such as calcite, barite and gypsum, that have formed exquisite crystals in the absence of heat or pressure. A notable example of this being the transparent crystals of gypsum known as selenite from the Oxford Clay and London Clay.

  
Transparent crystal of selenite (a variety of gypsum) from the London Clay of Essex

 

How crystals form To understand crystals we need to know about atoms. Atoms are the basic building blocks of everything around us, even the air we breath. The atoms that make up a mineral, and most other solid objects, are arranged in an orderly fashion, in other words the material has a crystalline structure. The shape of a crystal is an external expression of that internal, three-dimensional pattern. Different minerals have different internal arrangements of their atoms, which means that different minerals will form different shaped crystals. Quartz, for example forms hexagonal (six-sided) crystals with pointed ends, called terminations. There are thousands of different ways in which atoms can arrange themselves but these can be grouped into just a few basic patterns. There are, in fact, just 7 basic patterns of crystals called crystal systems. Quartz crystallises in the trigonal system, as does calcite. Crystals grow by adding layers of atoms, one layer at a time, each layer having the same pattern of atoms. In other words they do not grow from the inside outwards like an animal or plant, but grow chemically by the deposition of atoms from the outside. Once the supply of atoms of the material has been exhausted, for example if the hot fluid in a rock cavity drains away, the crystals lining the cavity just stop growing. Depending on the conditions deep underground different crystal faces may grow at different rates and the resulting crystals of a particular mineral may vary in shape but the angles between the faces are identical as this is set by the atomic pattern within. The natural crystals offered for sale on this website have flat crystal faces that formed because there was space for them to grow uninterrupted. When space is restricted, crystals will grow until they have entirely filled the space available and the result will be an intergrown mass of crystals without any natural crystal faces, much like sugar that crystallises in a jam-jar. Natural crystals can grow at different speeds, maybe almost instantly, maybe over millions of years - the rate of growth depends on the conditions and the supply of atoms and these vary greatly in the natural world. It is therefore rarely possible to tell how quickly a crystal grew.         Quartz crystals from Afghanistan

  

What are gemstones?

Gemstones are simply minerals which, when they are cut and polished, are suitable for jewellery or similar adornments. A gemstone must therefore be beautiful, and the most important factor here is its colour. It must also be durable, in other words hard enough to withstand handling and not easily scratched, although several soft minerals are cut as gemstones just for the collector. Of the 4,000 or so mineral species only about 50 are commonly used as gemstones. Some gemstones, such as jet and amber are of organic origin and therefore not strictly minerals. Organic materials such as ivory, pearls and coral are also considered gemstones but are not minerals.  

Gemstones are usually regarded as either precious or semi-precious. Nowadays, we regard diamond, ruby, sapphire and emerald as precious gemstones and all the others as semi-precious. The science of the study of gemstones is gemmology.

Click here to view gemstones for sale
 

Malachite from Africa - one of the most attractive gemstones


What are rocks?

 

Click here for a quick guide to rocks   Click here to view decorative stones for sale

As mentioned above, most rocks are simply mixtures of minerals although some, like pure marble, are made up of only one mineral, but this is unusual. The crystals of the various minerals that make up a type of rock can be readily visible, as in granite, or can be microscopic, as in basalt. Many rocks can be incredibly attractive, with beautiful colours and textures.  

Click on the image title opposite for a quick guide to rocks. 

 


Hertfordshire puddingstone - one of the World's most distinctive rocks
 

Looking after (and enjoying)
a mineral collection 

Click here for guidance on curating a collection

People purchase minerals or fossils for different reasons. Some may simply want a unique decorative ornament for the home, others may be adding to an existing collection. Whatever the reason for acquiring a geological specimen it is useful to remember that we are only temporary custodians of them and that we will eventually hand them on to others - perhaps the next generation. It is important therefore to look after them and to retain the information that came with them. 

Click on the image title opposite for advice on on taking care of, or curating, a geological collection, whether it is of rocks, minerals
or fossils. 

Recommended books

Some of these titles may be available for purchase through this website.
Please click here for details of books for sale.

  

General books on minerals, rocks and decorative stones

AGATES: TREASURES OF THE EARTH
By Roger Pabian, Brian Jackson, Peter Tandy and John Cromartie.  (2006). Published by the Natural History Museum, London.

AMBER: THE NATURAL TIME CAPSULE
By Andrew Ross. (2010). Published by the Natural History Museum, London.

CRYSTALS
By Gordon Cressey and Ian F. Mercer.  (Second edition 1999). Published by the Natural History Museum, London.

DECORATIVE STONE: THE COMPLETE SOURCEBOOK
By Monica Price. (2007). Published by Thames & Hudson.

FOSSILS, MINERALS AND ROCKS: COLLECTION AND PRESERVATION
By R. Croucher & A.R. Woolley. (1982).  Published by the British Museum (Natural History)/Cambridge University Press.
 
GEMSTONES: THE VISUAL GUIDE TO MORE THAN 130 GEMSTONE VARIETIES
By Cally Hall. (1994). Eyewitness Handbooks. Dorling Kindersley.
 
INTRODUCING GEOLOGY: A GUIDE TO THE WORLD OF ROCKS
By Graham Park. Third edition (2018). Published by Dunedin Academic Press Ltd.

INTRODUCING MINERALOGY
By John Mason. (2015). Published by Dunedin Academic Press Ltd.

ROCKS & FOSSILS: THE ULTIMATE GUIDE TO THE EARTH
By Arthur B. Busbey III et al. (1996). Published by Harper Collins.

ROCKS AND MINERALS: A UNIQUE PHOTOGRAPHIC GUIDE TO THE WORLD’S ROCKS AND MINERALS
By Monica Price & Kevin Walsh.  (2005). DK Pocket Nature.  Dorling Kindersley.

SAND: A JOURNEY THROUGH SCIENCE AND THE IMAGINATION
By Michael Welland. (2009). Oxford University Press.


                 

    ​​​​​​​    ​​​​​​​    ​​​​​​​          

  

  

A COLLECTOR'S GUIDE TO MINERALS, ROCKS AND GEMSTONES IN CORNWALL AND DEVON (Booklet)
By Cedric Rogers. (1968). Published by D. Bradford Barton Ltd.

AGATE COLLECTING IN BRITAIN
By Peter R. Rodgers. (1975). Published by Batsford.

A MINERALOGY OF WALES
By Richard E. Bevins. (1994). National Museum of Wales.

CRYSTAL MOUNTAINS: MINERALS OF THE CAIRNGORMS
By Roy E. Starkey. (2014). Published by British Mineralogy Publications.

DERBYSHIRE BLACK MARBLE (Booklet)
By John Michael Tomlinson. (1996). Published by the Peak District Mines Historical Society

​​​​​​​DERBYSHIRE BLUE JOHN (Booklet)
​​​​​​​By Trevor Ford. (Third edition - 2019). Published by East Midlands Geological Society.

DEVONSHIRE MARBLES (GA Guide No. 72) (Two volumes)
By Gordon Walkden. (2015). Published by the Geologists' Association

MINERALS OF BRITAIN AND IRELAND
By A.G. Tindle. (2008). Published by Terra Publishing.

MINERALS OF CORNWALL AND DEVON
By P.G. Embrey and R.F. Symes. (1987). Published by the British Museum (Natural History) .

MINERALS OF NORTHERN ENGLAND
By R.F. Symes and B. Young. (2008). Published by National Museums of Scotland/Natural History Museum.

MINERALS OF SCOTLAND: PAST AND PRESENT
By Alec Livingstone. (2002). Published by National Museums of Scotland

MINERALS OF THE ENGLISH LAKE DISTRICT: CALDBECK FELLS
By M.P. Cooper and C.J. Stanley. (1990). Published by Natural History Museum Publications.

MINERALS OF THE ENGLISH MIDLANDS
By Roy E. Starkey. (2018). Published by British Mineralogy Publications.

MINERALS OF THE PEAK DISTRICT
Edited by Mick Cooper. (1993). Published by Peak District Mines Historical Society.

SCOTTISH AGATES
By Nick Crawford and David Anderson. (2010). Published by Lapidary Stone Publications.

SERPENTINE (Booklet)
By M. Sagar-Fenton. (2005). Published by Truran Books.

THE LINDSAY GREENBANK COLLECTION: CLASSIC MINERALS OF NORTHERN ENGLAND
By Wendell E. Wilson. (2010). Published by Mineralogical Record Inc.

THE ROCKHOUND'S GUIDE TO THE PEAK NATIONAL PARK AND ADJACENT AREAS (Booklet)
By Don Edwards. (1975). Published by the Tideswell Dale Bookshop.

WHITBY JET (Booklet)
By H. Muller & K. Muller. (2009). Published by Shire Books.

​​​​​​​

                ​​​

​​​​      ​​​​​​​        ​​​​​​​​​​​​​​

            ​​​​​​​  ​​​​​​​

  ​​​​​​​ ​​​​​​​​​​​​​​​​​​​​​​   ​​​​​​​​   ​​​​​​​​​​​​​  

  

Recommended museums

 
 Sedgwick Museum of Earth Sciences 
Downing Street, Cambridge CB2 3EQ. Telephone: 01223 333456

Situated in the centre of Cambridge, the Sedgwick Museum has one of the World’s major collections of fossils. It also has a small but spectacular mineral gallery, displaying some of the finest specimens from its collection of more than 40,000 minerals and gemstones from around the world. Entry is free to the public. On the ground floor of the museum building, and open to the public only by appointment, is the John Watson Building Stone Collection, a magnificent collection of building stones, slates, polished marbles and ornamental stones from all over the world, displayed in their original early 20th century oak wall cases.

 Natural History Museum 
Cromwell Road,  London SW7 5BD.  Telephone: 020 7942 5000

The best place in Britain to see the immense diversity in the mineral kingdom is the magnificent Mineral Gallery on the first floor of London’s Natural History Museum. A staggering 14,000 specimens are on display here in their original 19^th century oak cabinets, representing nearly 2,000 mineral species.  It is probably the world's finest systematic display of minerals. If you include the specimens housed behind the scenes, the total collection of minerals in the museum numbers about 350,000 specimens which includes about 5,000 cut gemstones. It is one of the most important and comprehensive mineral collections in the world. In addition to this the museum houses a collection of rocks and decorative stones which consists of some 250,000 specimens.

On the ground floor of the museum is the British Geological Survey's London Information Office which sells geological maps and guides for the whole of the UK (open during office hours).

 Oxford University Museum of Natural History 
Parks Road,  Oxford OX1 3PW.  Telephone: 01865 272950

The collections of the Oxford University Museum of Natural History include over 30,000 mineral specimens and around 50,000 specimens of rocks and decorative stones. The museum itself is a spectacular neo-gothic building comprising many British stones. Of particular interest are the columns surrounding the central court; there are 30 separate columns here, each one of a different polished British decorative stone and inscribed with the name of the stone and its source. The museum also houses the Corsi Collection of Decorative Stones which was formed in the early 19^th century by Roman lawyer Faustino Corsi. It comprises 1,000 polished slabs, each of a different decorative stone. 

 

Print this page?   For a white background make sure your printer is set not to print backgrounds