School of rocks: Unlocking the Mineral Vault

As the Natural History Museum prepares to unlock its spectacular Mineral Vault, Helen Brown polishes up on geology and gemstones with Britain's King of Bling

Honeycomb nuggets of gold; glittering lozenges in pink, yellow or blue. Candy-cane crystals and molten-toffee slices of meteorite, shot through with chunks of green olivine. As visitors' eyes feast on the specimens in the Natural History Museum's new Mineral Vault, they may feel like they are surrounded by the world's most expensive pick'*'mix.

On the day I visit, the curator of minerals, Alan Hart, is putting the final touches to the displays. He is the man with the key to all the cases, and he lifts diamonds and rubies to the light for us to admire. The visual distraction allows me to ask a couple of embarrassingly basic questions. First: what's the difference between a rock and a mineral?

"A mineral is a naturally occurring chemical compound," says Hart. "There are about 4,500 known in the world – we call them 'species'. A rock is made of lots of minerals together. Although, confusingly, some are just composed of just one [monomineralic], most are an amalgamation of about 10."

The super-secure Mineral Vault showcases the best specimens in the museum's collection. It places cut and set gemstones alongside their naturally occurring forms. "Mineralogy is a science with its roots in chemistry, but it's so deeply entangled with cultural history and art," says Hart. "Our subjects are so beautiful, interesting and often sculptural. As their values and uses have changed over time, they tell us as much about the nature of our own species as they do about themselves. We preserve many of these samples as objects – we wouldn't work or experiment on them."

Carefully lifting the diamond-starred Murchison snuffbox from its case, Hart talks about the history of diamonds. They are carbon allotropes that take their names from the greek adamas, meaning invincible, and tell us a great deal about the conditions of our planet's formation.

"Seventy-five per cent of the diamonds in the world are 3 billion years old," says Hart. They're formed from carbon under extreme pressure of between 45 and 60 kilobars, but at a comparatively low temperature range of between 900deg and 1,300deg. Such conditions exist in only two places on Earth: in the lithospheric mantle below continental plates, and at the site of meteorite strikes.

Other treasures in the museum's mineralogic chest hail from those same meteors. Dr Caroline Smith, the curator of meteorites, tells me that between 40,000 and 60,000 tonnes of space rock hits the earth each year, although "most of that mass is made up of tiny dust specks. And most fall into the sea. We do get around 1,000 basketball-sized meteorites a year, too."

Many of the stones that Hart raises lovingly to the light have names that would befit a footballer's wife: Sherry Topaz, Pink Beryl and Watermelon Tourmaline. "The complex chemistry of tourmaline meant that this one started off as a nice red crystal (rubelite)," he explains, "and then the chemistry of the contributing fluids change – there might have been slightly more iron – and that absorbs the light differently to give us the green."

He reaches for a gem that resembles a fruity cocktail fused into a glittering ice cube. "This is one of our treasures," he says. "Padparadscha – an orange sapphire with a hint of pink. Stones of this quality are very rare. Usually you'd see them with one or two carats. This one is 57. Some of the rarest things we have are rubies as they come out of the ground," he gestures towards a slab of rich, murky red. "Burma is the place with the finest rubies – called 'pigeon's blood' rubies."

Downstairs, Hart clicks open a safe to hand me a chunk of gold called the La Trobe Nugget. As I feel the soft metal, he explains that it is "one of the finest crystalline golds in the world – look at the cubes in it. They're rounded, but grow from octahedrons – a cubic structure. And come look at the alexandrite..."

Hart is a bit like Gollum, with his "precious", but this is one of the best specimens of alexandrite ever found. As he holds it up to the light pouring in through the window, it appears green. Put it under artificial light, however, however, and it does a little magic trick – it glows a beetroot red. "We were experimenting with this bit this morning," he says. Scientists are still studying why light frequencies cause this effect in the stone.

Minerals could hold the key to all sorts of future technological advances. We all know that diamonds – once valued only for their beauty – turned out to be the ultimate mining tools, and have properties that are now seeing them used in groundbreaking medical techniques and in electronics. " There are always new uses for minerals," says Hart. Some minerals, such as asbestos, seem to promise much, then turn out to have hidden dangers. "But who would have thought, 100 years ago, that a mineral like silicon would be everywhere today, so essential to our daily lives?"

Set in stone: highlights from the Mineral Vault

This world-class collection of 296 naturally coloured diamonds has been loaned to the Natural History Museum by collectors Alan Bronstein and Harry Rodman. It comprises 267.45 carats of exceptionally rare stones from the 12 colour varieties, from emerald green to blood red. The display highlights a property shared by coloured and white diamonds – some glow and change colour when exposed to ultraviolet light.

1. La trobe Gold Nugget

Charles Joseph La Trobe, lieutenant-governor of the state of Victoria, Australia, was visiting the McIvor gold mine when word came that an unusually large nugget had been found and named in his honour. although small as nuggets go, it is one of the largest crystalline-fold specimens in existence. Some of the cubes are more than half an inch wide, and the whole is comprised of a mass of crystals. The richness of the colour is due to a small impurity of copper. Gold is one of the few metals found in nature that is generally untainted with other elements. Crystal forms are extremely rare – and this cluster of intergrown cubic crystals is one of the world's finest examples.

2. Alexandrite

Discovered in 1830 in Russia, alexandrite is a stone that changes colour – generally, from green to red. Since these were the Russian imperial colours, it was named after the Tsar Alexander II. Alexandrite emerged millions of years ago in a metamorphic environment. Its formation required specific geological conditions: the elements beryllium and chromium – the colouring agent in alexandrite – have contrasting chemical characteristics and do not, as a rule, occur together. A deficiency of silica, the second most common element in the Earth's crust, is also required. This geological scenario has occurred only rarely in the Earth's history and, as a result, alexandrite crystals are extremely rare.

3. Morganite

Morganite is the term for pink beryl (yellow being "heliodor", green "emerald" and blue "aquamarine". Beryl forms in prismatic crystals that can vary hugely in size: one weighing 200 tons and measuring 20ft was mined in Brazil. Beryl is the main commercial ore of beryllium – a metal used to make corrosion resistant springs, electrical contacts and cladding for nuclear fuel elements.

4. Boulder Opal

Opals range in colour from fiery red to deep black. What they all have in common is a bewitching flash of rainbow colours, or iridescence. This inspired an Aboriginal legend that their creator came to earth on a rainbow, to bring peace to humanity. Opals are 5-10 per cent water and some may crack if left to dry out too quickly. The iridescence is caused by the reflection and scattering of light from minute, uniform and closely packed silica spheres. Since the late 19th century, Australia has been the principal source of black and white opals.

5. Topaz

It is widely believed to have derived its English name from the Sanskrit word "tapas" meaning "fire". Topaz forms in igneous rocks such as granite and pegmatite and may also be found in waterworn pebbles in alluvial sands. Some of the most sought after topaz gemstones contain tear shaped internal cavities containing immiscible gas bubbles or liquid.

6. Siderite Cube

Known affectionately as "The Box" at the Natural History Museum, this sculptural cube of the iron carbonate siderite was found in Devon's Virtuous Lady Mine (named after Elizabeth I) in the early 1830s. " What's so great about this specimen," says Hart, "is that it's an example of chemistry at work in the Earth and it's a geological mystery. The siderite would have formed around fluorite crystals. Those are very hard. Siderite is relatively soft. So the question is: what circumstances caused the fluorite to dissolve and leave the lovely, fairy-box siderite? It's the reason we opened the Mineral Vault. Maybe some eight-year-old girl or boy will see it and be inspired to solve the riddle."

7. Padparadscha

This exotic name is given to a rare type of sapphire that has a delicate, orange-pink hue. The colour of a true padparadscha is disputed: if it is too orange, it is merely an orange sapphire. The perfect colour is that of a Sri Lankan sunset. Hard-wearing and heat-resistant, sapphires of every shade have been mined for use in the mechanisms of clocks and measuring instruments. They are also used in window apertures and the nibs of ball-point pens.

The exhibition opens on 28 November

voicesGood for Lana Del Rey for helping kill that myth, writes Grace Dent
The Pipes and Drums of The Scottish Regiments perform during the Opening Ceremony for the Glasgow 2014 Commonwealth Games at Celtic Park on July 23, 2014 in Glasgow, Scotland.
Commonwealth GamesThe actor encouraged the one billion viewers of the event to donate to the children's charity
Karen Dunbar performs
Entertainers showcase local wit, talent and irrepressible spirit
Members of the Scotland deleagtion walk past during the opening ceremony of the 2014 Commonwealth Games at Celtic Park in Glasgow on July 23, 2014.
Arts and Entertainment
The Tour de France peloton rides over a bridge on the Grinton Moor, Yorkshire, earlier this month
Life and Style
fashion Designs are part of feminist art project by a British student
Very tasty: Vladimir Putin dining alone, perhaps sensibly
Life and Style
Listen here: Apple EarPods offer an alternative
techAre custom, 3D printed earbuds the solution?
Arts and Entertainment
Top guns: Cole advised the makers of Second World War film Fury, starring Brad Pitt
filmLt-Col Steven Cole is the man Hollywood calls when it wants to borrow a tank or check a uniform
The University of California study monitored the reaction of 36 dogs
sciencePets' range of emotions revealed
Snoop Dogg pictured at The Hollywood Reporter Nominees' Night in February, 2013
people... says Snoop Dogg
ebookA unique anthology of reporting and analysis of a crucial period of history
Arts and Entertainment
A scene from Shakespeare in Love at the Noel Coward Theatre
theatreReview: Shakespeare in Love has moments of sheer stage poetry mixed with effervescent fun
Joining forces: young British men feature in an Isis video in which they urge Islamists in the West to join them in Iraq and Syria
newsWill the young Britons fighting in Syria be allowed to return home and resume their lives?
Arts and Entertainment
The nomination of 'The Wake' by Paul Kingsnorth has caused a stir
Life and Style
food + drinkZebra meat is exotic and lean - but does it taste good?
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

BI Manager - £50,000

£49000 - £55000 per annum + competitive: Progressive Recruitment: My client is...

BI Project Manager - £48,000 - £54,000 - Midlands

£48000 - £54000 per annum + Benefits package: Progressive Recruitment: My clie...

VB.Net Developer

£35000 - £45000 per annum + competitive: Progressive Recruitment: If you're pa...

SAP Business Consultant (SD, MM and FICO), £55,000, Wakefield

£45000 - £55000 per annum + competitive: Progressive Recruitment: SAP Business...

Day In a Page

Screwing your way to the top? Good for Lana Del Rey for helping kill that myth

Screwing your way to the top?

Good for Lana Del Rey for helping kill that myth, says Grace Dent
Will the young Britons fighting in Syria be allowed to return home and resume their lives?

Will Britons fighting in Syria be able to resume their lives?

Tony Blair's Terrorism Act 2006 has made it an offence to take part in military action abroad with a "political, ideological, religious or racial motive"
Beyoncé poses as Rosie the Riveter, the wartime poster girl who became a feminist pin-up

Beyoncé poses as Rosie the Riveter

The wartime poster girl became the ultimate American symbol of female empowerment
The quest to find the perfect pair of earphones: Are custom, 3D printed earbuds the solution?

The quest to find the perfect pair of earphones

Earphones don't fit properly, offer mediocre audio quality and can even be painful. So the quest to design the perfect pair is music to Seth Stevenson's ears
US Army's shooting star: Lt-Col Steven Cole is the man Hollywood calls when it wants to borrow a tank or check a military uniform

Meet the US Army's shooting star

Lt-Col Steven Cole is the man Hollywood calls when it wants to borrow a tank or check a military uniform
Climate change threatens to make the antarctic fur seal extinct

Take a good look while you can

How climate change could wipe out this seal
Should emergency hospital weddings be made easier for the terminally ill?

Farewell, my lovely

Should emergency hospital weddings be made easier?
Man Booker Prize 2014 longlist: Crowdfunded novel nominated for first time

Crowdfunded novel nominated for Booker Prize

Paul Kingsnorth's 'The Wake' is in contention for the prestigious award
Vladimir Putin employs a full-time food taster to ensure his meals aren't poisoned

Vladimir Putin employs a full-time food taster

John Walsh salutes those brave souls who have, throughout history, put their knives on the line
Tour de France effect brings Hollywood blockbusters to Yorkshire

Tour de France effect brings Hollywood blockbusters to Yorkshire

A $25m thriller starring Sam Worthington to be made in God's Own Country
Will The Minerva Project - the first 'elite' American university to be launched in a century - change the face of higher learning?

Will The Minerva Project change the face of higher learning?

The university has no lecture halls, no debating societies, no sports teams and no fraternities. Instead, the 33 students who have made the cut at Minerva, will travel the world and change the face of higher learning
The 10 best pedicure products

Feet treat: 10 best pedicure products

Bags packed and all prepped for holidays, but feet in a state? Get them flip-flop-ready with our pick of the items for a DIY treatment
Commonwealth Games 2014: Great Scots! Planes and pipers welcome in Glasgow's Games

Commonwealth Games 2014

Great Scots! Planes and pipers welcome in Glasgow's Games
Jack Pitt-Brooke: Manchester City and Patrick Vieira make the right stand on racism

Jack Pitt-Brooke

Manchester City and Patrick Vieira make the right stand on racism
How Terry Newton tragedy made iron men seek help to tackle their psychological demons

How Newton tragedy made iron men seek help to tackle their psychological demons

Over a hundred rugby league players have contacted clinic to deal with mental challenges of game