Spinel

Spinel is a special stone.

Its name comes from a word for a spine. This is because its crystals have points.

These stones come in many colors. They can be red, blue, or green. They can even be yellow or black.

A little bit of metal makes them red. A little bit of cobalt makes them blue.

Some spinels are very famous. They are part of royal crowns. One large spinel is the biggest in the world.

Spinel is a beautiful mineral.

Its name comes from a Latin word for spine. This is because its crystals often have points. Spinel can be many colors. It can be red, blue, green, or black. It can also be brown, yellow, or lavender. Small bits of metal change its color. Chromium makes some spinels red. Cobalt makes some spinels blue.

Some spinels are very famous. They are kept in royal crowns. The Black Prince's Ruby is a famous spinel. Many people once thought it was a real ruby. Scientists now know it is spinel. Spinel is a hard stone. It has a hardness of 8. It can be clear or cloudy. It can also look shiny like glass.

Spinel forms in many places. It forms in rocks deep inside the Earth. It is also found in meteorites from space. People can make spinel in labs. This is called synthetic spinel. It is used for jewelry. It is also used for military tools. This is because it is very strong against pressure.

Spinel is a special kind of mineral.

It belongs to a large group of minerals called the spinel group. The name comes from a Latin word that means a small spine. This is because the crystals often have sharp points. Spinel can be many different colors. It might look red, blue, green, or even black. It can also be yellow, brown, or lavender.

These colors happen because of tiny bits of other things inside the mineral. For example, chromium makes some spinels a bright red color.

This mineral forms in several ways deep inside our world. It is often found in metamorphic rocks like limestone. It can also grow in certain types of igneous rocks. In these rocks, magmas interact with other rocks to create it. Some spinel also lives very deep in the Earth's mantle. It can be found between 20 and 120 kilometers down. Even more amazing, spinel is found in some meteorites from space. These are called chondritic meteorites. They contain small bits of spinel called CAIs.

People have valued spinel for a very long time. In the past, people sometimes called red spinel a "balas ruby." This name came from a place called Badakhshan. That region is in central Asia. For many years, this area was the main place to find red spinels. Some spinels are part of famous royal treasures. The Black Prince's Ruby is in the British Crown Jewels. The Timur Ruby is also a very famous gemstone. There is even a huge spinel called the Samarian Spinel. It is the largest one known in the world.

Many different places on Earth hold these gems. You can find them in the gravel of Sri Lanka. They are also found in Afghanistan and Tajikistan. In recent years, people found colorful spinels in many new spots. Some are found in Vietnam, Tanzania, and Kenya. In 2018, scientists found bright blue spinels in Canada. This blue color comes from a small amount of cobalt. This shows how much the tiny parts inside change the whole stone.

Today, we can also make spinel in a lab. This is called synthetic spinel. Scientists use methods like the Verneuil method to make it. They can even make it in flat sheets. Synthetic spinel is often used for jewelry. It is the birthstone for the month of August. This stone is also very strong against pressure. Because it is so tough, it is used for military tools. It is much stronger than regular glass.

Spinel is a significant mineral belonging to a large group known as the spinel group.

It is specifically the magnesium/aluminium member of this group. The mineral has a chemical formula of MgAl2O4. This means it is made of magnesium, aluminium, and oxygen. Its name comes from the Latin word "spina," which is a diminutive form of spine. This name refers to the pointed shape of its crystals. Spinel is highly valued because it can appear as a beautiful gemstone. It belongs to the cubic crystal system, which means its internal structure is very organized.

The physical structure of spinel is quite distinct. It crystallizes in the isometric system, often forming octahedra, which are eight-sided shapes. These crystals are usually twinned, meaning two crystals grow together. Spinel does not have true cleavage, which is the way a mineral breaks along flat planes. Instead, it shows an octahedral parting and a conchoidal fracture. A conchoidal fracture is a break that looks curved, like the inside of a seashell. The mineral has a hardness of 8 on the Mohs scale. It also has a specific gravity ranging from 3.5 to 4.1. Its luster can be described as vitreous, meaning glass-like, or it can be dull.

Colors in spinel are caused by small additions of other elements. While it can be colorless, it is usually found in shades of red, lavender, blue, green, brown, black, or yellow. For example, chromium(III) is responsible for the red color in spinels from Burma. On the other hand, small additions of cobalt create a pure blue coloration. These chemical variations are why spinel can appear in so many different hues. Because of these colors, many spinels are used as precious gemstones. They can range from being completely transparent to being opaque.

Spinel forms through several different geological processes. It is a metamorphic mineral, meaning it forms when existing rocks change due to heat and pressure. It is often found in metamorphosed limestones and silica-poor mudstones. It also appears as a primary mineral in rare mafic igneous rocks. In these rocks, the magmas are deficient in alkalis compared to aluminium. In such environments, aluminium oxide may form as the mineral corundum. Alternatively, the aluminium may combine with magnesia to form spinel. This chemical relationship is why spinel and ruby are frequently found together.

The mineral also exists deep within the Earth's interior. Spinel is common in peridotite in the uppermost mantle. This occurs at depths between approximately 20 km and 120 km. The exact depth can change depending on the chromium content. At shallower depths, above the Moho, a different mineral called calcic plagioclase is more stable. Deeper in the mantle, below the spinel stability region, garnet becomes the stable phase. Spinel is also found in space. It is a common mineral in calcium-aluminum-rich inclusions, or CAIs, found in some chondritic meteorites.

Historically, spinel has been confused with other gems like rubies. Before modern science defined a "ruby," transparent red spinels were called spinel-rubies or balas rubies. The name "balas" comes from Balascia, the ancient name for Badakhshan. This is a region in central Asia located in the upper valley of the Panj River. The name Balascia may even come from the Sanskrit word for "crimson-coloured morning sun." Many famous gemstones are actually spinels. These include the Black Prince's Ruby and the Timur Ruby in the British Crown Jewels. The Samarian Spinel is the largest known spinel in the world, weighing 563 carats.

Today, humans can create synthetic spinel in laboratories. Scientists use methods like the Verneuil method or the flux method pioneered by Edmond Frémy. Some transparent spinel is even made in sheets through a process called sintering. Synthetic spinel is often used as an inexpensive gemstone for August birthstone jewelry. Light blue synthetic spinel can imitate aquamarine beryl. Green synthetic spinel can be used to simulate emerald or tourmaline. Because synthetic spinel is much stronger against pressure than glass, it also has applications in military and commercial uses.