The James Webb Space Telescope[3] will have 18 hexagonal beryllium sections for its mirrors.

Because JWST will face a temperature of −240 degrees Celsius (30 kelvins), the mirror is made of beryllium, a material capable of handling extreme cold better than glass.

Beryllium contracts and deforms less than glass — and thus remains more uniform — in such temperatures.

Beryllium is also used in the Joint European Torus fusion research facility, to condition the plasma facing components.[4]

Beryllium has also been used in tweeter construction by the company Focal-JMlab on its flagship Utopia Be series as an alternative to titanium and aluminium, largely due to its lower density and greater rigidity.[5]

From this sweet salt,
I will make you emeralds
and aquamarine. From this
pale metal, I will forge you
glass that will not melt.

Let me take this sweet
bivalent and make of it
an instrument that spins
to tell us where we are.
Let me form a cord of it

to run between your lips
and mine, so we can talk
to one another faster
than sound has ever
traveled before.

I got an atomic number of 4
And I am quite a bore
I’m not very fast
But I sure can scratch glass

I am from the Greek
And once referred to as sweet
I am very light-weight
So please, don’t use me as a paper weight

Name: Beryllium

Symbol: Be

Atomic Number: 4

Atomic Weight: 9.012182

Family: Alkaline Earth Metals

CAS RN: 7440-41-7

Description: Strong, hard, gray-white metal. Lightest rigid metal. Formerly called glucinium (Gl).