ROCKS
PRECIOUS
GEMS & MINERALS
A fabulous collection of rocks, gems and
minerals, gathered from all over the earth.
Items shown may change due to circumstances beyond our control
Authentic pieces gathered by our specialists from all corners of the earth.
The world’s most beautiful rocks,
gems and minerals for you to treasure
A collection
to share with
all the family
Obsidian
UNITED STATES
Aragonite
MOROCCO
Lapis lazuli
AFGHANISTAN
Hornblende
CHINA
· Full-size samples
· Wonderful variety
· Spectacular display
Chyrsoprase
AUSTRALIA
Opal
Items shown may change due to circumstances beyond our control
. The most fascinating rocks, gems and
minerals of our planet, including amethyst,
rose quartz, agate and tiger’s eye
. Learn how to identify them, how they were
formed and where to find them in every issue
of your magazine, and in the comprehensive
A-Z cards that accompany the collection.
. Protect your precious collection in
exclusive and specially designed
display boxes.
Don’t miss out on this
unique collection!
Since it was founded in 1888, this scientific and educational not-for-profit
organisation has supported more than 9,000 explorations and research
projects, contributing to our knowledge of land, sea and space.
FREE
display box for
your collection
This mineral has amazing optical
properties. Looking through it is like
having double vision.
ICELAND SPAR
According to legend, a Greek shepherd discovered
this mineral when he noticed the nails in his
sandals were sticking to the rocks. It is a natural
magnet that attracts iron.
MAGNETITE
In dry conditions, gypsum crystals grow
so that they resemble petals. These
beautiful formations are like blossoms
set in stone.
DESERT ROSE
This form of muscovite, or common
mica, owes its intense green colour
to the chromium oxide it contains. It is
often found alongside emeralds.
FUCHSITE
This form of iron sulphide is
sometimes called ‘fool’s gold’, due
to the way it sparkles and glistens.
PYRITE
Amazing minerals…
Used by the Romans to make cement,
this mineral dissolves in acidic water and
forms stalactites and stalagmites in caves.
CALCITE
Did you know?
• A mineral is a natural substance, found on the surface
or within the layers of the earth’s crust.
This purple crystalline mineral is a
sought-after variety of quartz and has been used
as a gem for centuries.
AMETHYST
CHALCEDONY GEODE
Formed inside cavities in rocks,
these are like miniature crystal
caves and highly prized in
collections.
The quality of this aggregate of different
minerals is dependent on the proportion of
lazurite, which produces the intense blue colour.
LAPIS LAZULI
Also known as the stone of the Amazon, this
rare mineral’s rich blue-green colour has
made it highly valued by collectors.
AMAZONITE
TIGER’S EYE
A variety of quartz with a unique appearance,
this gemstone is distinctive due to its beautiful
layers of colour and characteristic sheen.
…and stunning gemstones
One of the most sought-after precious
stones, this is a variety of beryl. It
owes its green hue to the chromium or
vanadium within it.
EMERALD
Did you know?
• A gem or precious stone is a rock or mineral that can be cut
and polished to use in jewellery making or arts and crafts.
Man-made versions are created with resins and pigments.
Playing an important role in
Buddhism, and in Feng-Shui, this
stone is said to represent purity,
innocence and integrity.
Discover why the world of geology has fascinated man since the dawn of time, with these
fact-packed magazines and A-Z reference cards, developed by experts and designed for
the whole family to use.
MINERALS
GEMS
PLANET EARTH
MINERALS AND MAN
AROUND THE WORLD
COLLECTING
GUIDE TO MINERALS
YOUR MAGAZINE SECTIONS
Everything you need to know
about the world of precious
rocks, gems and minerals
BlUE
agaTE
2 3 5 4 1Blue agate
SiO
2B
lue agate, a sub-variety of quartz, is a very attractive gem with concentric bands alternately coloured blue and white. Its beauty depends on both the intensity and the extent of its blue colour. Blue agate forms in volcanic rocks infiltrated by hot silica (SiO2) solutions. Variations in the dissolved impurities and the conditions in which the minerals are deposited give rise to the different layers. If the solution cools slowly, quartz macrocrystals can form in the central section. If cooling is rapid, however, the crystals that form are microscopic.naRTIFIcIal coloUR
Many of the blue agates offered for sale to collectors are artificially coloured, having been impregnated in a vacuum with a blue dye solution. This solution penetrates the network of quartz microcrystals to a lesser or greater extent according to the porosity of the
mineral bands. The best way of distinguishing natural agates from treated ones is to examine the uniformity and clarity of their blue colouring, as both of these properties are better defined in natural agates.
nTHE BUDDHIST MInERal
Nowadays, agate (particularly blue agate) is highly prized in China and India, owing to the importance of the stone in Buddhism and its role in feng shui. In the West, blue agate was a much sought-after gem during the Renaissance. This period gave rise to the majority of blue agate cameos, which were extremely finely cut. Due to their great beauty and historic importance they remain highly valuable today.
Where it is found:
The most outstanding pieces of blue agate come from mines
in Asia, Africa and the Americas, specifically: 1. Brazil (Minas
Gerais), 2. Uruguay (Artigas), 3. China (Tibet), 4. Mexico
(Chihuahua), and 5. Democratic Republic of Congo.
class Oxides and hydroxides System Trigonal crystal Hardness 7 Fracture Conchoidal Exfoliation None lustre Vitreous Streak White onyx.indd 2 6/9/10 12:42:12
CARDS
Plate tectonics:
in constant motion
1 4 5 3T
he theory of plate tectonics was developed by a number ofpeople at the end of the 1960s and in the early 1970s. It explains most of the geological processes that take place on Earth. The development of the oceans and continents, the location and types of volcanoes and earthquakes, the formation of mountain ranges or places where there is sedimentation are all processes explained by this theory. According to the theory of plate tectonics, the Earth is divided into rigid plates which move on top of another, more fluid, layer called the asthenosphere, or upper mantle. The plates vary greatly in thickness, from a few kilometres in parts of the ocean basins to up to 20 km beneath large mountain ranges. As the plates move some pull apart, whereas others collide. Still more move sideways, sliding past one another.
Plates separate: oceanic ridges
Where plates pull apart beneath the ocean submarine mountain ranges form. Running down the centre of these ranges are deep fissures through which magma continuously flows. As this magma hardens it forms new rock, which is added to the separating edges of the plates.
1
Plates collide: collision of a continental and an oceanic plate
Oceanic plates are thinner and more dense than continental plates. When the two collide, the oceanic plate is subducted. The magma produced by this process rises through the continental plate forming mountains and volcanoes. The Andes was formed by this type of collision.
5
Plates collide: collision of two continental plates
When two continental plates collide they thicken at their edges, creating huge mountain ranges. The Himalayas was formed in this way. Here, the thickened crust prevents magma from reaching the surface. Instead, it cools within the newly created mountain chain.
3
Hot spots
Sometimes hot material rises from the centre of the Earth and raises the temperature of the underside of a plate, producing magma. This process leads to volcanic activity both on land and beneath the ocean.
Oceanic trenches
In places where one oceanic plate sinks beneath another plate (subduction), trenches form. These trenches may reach depths of more than 10 km.
Plumes
Beneath the oceanic ridges columns of magma called ‘plumes’ emerge from great depths. These spill out to form the underwater mountain ranges of the ridges themselves and in places break through the surface of the sea to form volcanic islands, such as Iceland.
The outermost part of the Earth (its crust) consists of a series of rigid plates that are in constant movement. This movement is almost imperceptible to us, ranging from about 2 to 6 cm a year. Although this movement may seem insignificant, over millions of years continental masses can split
and may become separated by thousands of kilometres.
2
Plates move sideways: transform faults
There are places where plates neither collide nor separate, but instead move sideways past each other. These places are called transform faults. Most transform faults occur beneath the ocean’s surface. The fault between the Iberian Peninsula and north Africa is of this type.
2
Plates collide: collision of two oceanic plates
When most plates collide, one sinks beneath the other in a process called ‘subduction’. As it sinks it melts and the magma generated rises to the surface, where it erupts from volcanoes. Where subduction occurs beneath the ocean island chains are created by these volcanoes, marking the boundary. The Japanese archipelago and the Philippines are both examples of this kind of volcanic island chain.
4 3
Extremes of height and depth
Diagram comparing the height of the Himalayas with the depth of the
Marianas Trench 11.022 m
8.850 m
Sea level
4
5
Plate tectonics: in constant motion
45
PLANET EARTH
