Name: The most colorful gemstones on Earth - Jeff Dekofsky
Uploaded: 2020-12-03T19:00:10.000Z
Duration: 5 min 56 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

On an auspicious day  in November of 1986,

5 Australian miners climbed Lunatic Hill—

so named for the mental state  anyone would be in to dig there.

While their competitors searched  for opals at a depth of 2 to 5 meters,

the Lunatic Hill Syndicate bored  20 meters into the earth.

And for their audacity, the earth rewarded them

after the much larger rocky, icy body flying by the earth at that time.

The Halley's Comet opal is a marvel, but its uniqueness is, paradoxically,

While diamonds, rubies, emeralds, and other precious stones

thanks to a characteristic  called "play of color."

This shimmering, dazzling, dancing display of light

comes about from a confluence  of chemistry, geology, and optics

that define opals from their earliest moments, deep underground.

It's there that an opal begins its life as something surprisingly abundant: water.

Trickling down through gaps  in soil and rock,

water flows through sandstone, limestone, and basalt,

picking up a microscopic compound called silicon dioxide.

This silica-enriched water enters the voids inside pieces of volcanic rock,

prehistoric river beds, wood  and even the bones of ancient creatures.

Gradually, the water starts to evaporate,

and the silica-solution begins forming a gel,

within which millions of silica spheres form layer by layer

The gel ultimately hardens  into a glass-like material,

and the spheres settle into a lattice structure.

The vast majority of the time, this structure is haphazard,

resulting in common, or potch, opals with unremarkable exteriors.

The tiny, mesmerizing percentage  we call precious opals

have regions where silica beads of uniform size form orderly arrays.

So why do those structures produce such vibrant displays?

The answer lies in a principle of wave physics called interference.

let's look at what happens  when a single color of light—

green, with a wavelength of 500 nanometers— hits a precious opal.

The green light will scatter throughout the gemstone

and reflect back with varying intensities—

from most angles suffused,  from some entirely dimmed,

What's happening is, some of the green light reflects off of the top layer.

Some reflects off of the layer below that.

When the additional distance it travels from one layer to the next, and back,

is a multiple of the wavelength— such as 500 or 1000 extra nanometers—

the crests and valleys of the waves  match each other.

This phenomenon is called  constructive interference,

and it amplifies the wave, producing a brighter color.

So if you position your eye  at the correct angle,

the green light reflecting from many layers adds together.

and you change the distance  the light travels between layers.

Change it enough, and you'll reach a point where the crests match the valleys,

making the waves cancel each other out— that's destructive interference.

Different colors have different wavelengths,

which translates to varying distances  they have to travel

That's why colors roughly correspond to silica bead sizes.

The spaces between 210 nanometer beads are just right to amplify blue light.

For red light, with its long wavelengths,

the silica beads must be close to 300 nanometers.

Those take a very long time to form, and because of that,

The differences in the arrangements  of the gel lattices

within a particular stone result in a wide range of color patterns—

everything from broad flash  to pin-fire to the ultra-rare harlequin.

The circumstances that lead  to the formation of precious opal

are so uncommon that they only occur in a handful of places.

where an ancient inland sea created the perfect conditions.

It was there that the Halley's Comet opal formed some 100 million years ago.

Which raises the question:  in the next 100 million years,

silica-rich water will percolate  through the nooks and crannies

of some of the discarded artifacts  of human civilization.

What opalescent plays of light  will one day radiate

from the things we forget in the darkness?