Diamonds, sapphires, rubies, and emeralds are considered precious and all other gemstones are semi-precious.

Precious stones are distinguished by their quality, their rarity and the beauty of their colours. There are only four precious stones: diamond, sapphire, ruby and emerald. All other stones are therefore called semi-precious stones.

Diamond, ruby, sapphire and emeralds are all classed as precious stones and all other stones are considered semi-precious stones. This difference was distinguished in ancient times when these stones were viewed as rare and valuable.

What is the most expensive metal in the world?

• The most expensive metal in the world is Californium.
• Of far more practical application than californium and second to it, rhodium is the second-most expensive metal.
• Iridium is one of the rarest naturally occurring elements, which accounts for its high price.

Universe’s oldest known quasar discovered 13 billion light-years away. Astronomers have found the farthest known source of radio emissions in the universe: a galaxy-swallowing supermassive black hole.

According to the Mohs Hardness Scale, tooth enamel earns a 5. That means it’s about as hard, or harder, than steel. For reference, diamonds are the strongest substance on earth, ranking 10 on the Mohs scale.

Diamond is harder than obsidian, as obsidian is a form of volcanic glass. Obsidian has a hardness of 5 to 5.5 on the mineral hardness scale, whereas diamonds have a hardness of 10.

Because “hardest” is not the same as “indestructible.” It’s absolutely possible to break, crack, or otherwise damage a diamond–jewelers, after all, are able to cut a diamond into those lovely facets we all adore.

As an example, you can scratch steel with a diamond, but you can easily shatter a diamond with a hammer. The diamond is hard, the hammer is strong. Hit steel with a hammer of any material and it just absorbs the blow by shifting the ions sideways instead of shattering.