Spinel in the context of "French crown jewels"

The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about 10 km (6.2 mi) under the oceans, and about 35 km (22 mi) under the continents) and ends at the top of the lower mantle, at about 670 km (420 mi). Temperatures range from around 900 K (627 °C; 1,160 °F) at the upper boundary with the crust to around 1,200 K (930 °C; 1,700 °F) at the boundary with the lower mantle. Upper mantle material that has come up onto the surface comprises about 55% olivine, 35% pyroxene, and 5–10% of calcium oxide and aluminum oxide minerals such as plagioclase, spinel, or garnet, depending on depth.

Circumstellar dust is cosmic dust around a star. It can be in the form of a spherical shell or a disc, e.g. an accretion disk. Circumstellar dust can be responsible for significant extinction and is usually the source of an infrared excess for stars that have it. For some evolved stars on the asymptotic giant branch, the dust can be composed of silicate emissions. According to a study, it is still uncertain whether the dust is a result of crystalline silicate or polycyclic aromatic hydrocarbon. However, recent observations revealed that Vega-type stars display broad silicate emission. It is suggested that the circumstellar dust components can depend on the evolutionary stage of a star and is related to the changes in its physical conditions.

The study of the composition of this dust is dubbed astrominerology. The circumstellar dust around aging stars has been observed to include, "almost pure crystalline Mg-rich silicates (forsterite and clinoenstatite), amorphous silicates, diopside, spinel, oxides (corundum and Fe0.9Mg0.1O), and also carbon-rich solids such as: (hydrogenated) amorphous carbons, aromatic hydrocarbons and silicon carbide."

The Imperial State Crown is the state crown of the British monarch. Based on the design of Queen Victoria's Crown of 1838, which had fallen into disrepair, it was made in 1937 for the coronation of King George VI. The crown remains in use today at coronations and State Openings of Parliament. It is adorned with 3,170 precious stones, including the 317-carat (63 g) Cullinan II diamond, St Edward's Sapphire, the Stuart Sapphire, and the Black Prince's Ruby (a large red spinel).

The Black Prince's Ruby is a large, irregular cabochon red spinel weighing 170 carats (34 g) set in the cross pattée above the Cullinan II diamond at the front of the Imperial State Crown of the United Kingdom.

The spinel is one of the oldest gems in the Crown Jewels of the United Kingdom, with a history dating back to the mid-14th century. According to a legend originating from the 1760s, the stone has been in the possession of the English and later British monarchy since it was given in 1367 by the Spanish king Peter of Castile to the then Prince of Wales, Edward of Woodstock, known as the "Black Prince". Henry V is said to have worn it at the Battle of Agincourt in 1415. The stone is believed to have been mined in Badakhshan in present day Afghanistan, the principal source of large spinel gems in the Middle Ages.

The Three Brothers (also known as the Three Brethren; German: Drei Brüder; French: Les Trois Frères) was a piece of jewellery created in the late 14th century, which consisted of three rectangular red spinels arranged around a central diamond. The jewel is known for having been owned by a number of important historical figures. After its commission by Duke John the Fearless of Burgundy, the jewel was part of the Burgundian crown jewels for almost 100 years, before passing into the possession of German banker Jakob Fugger.

The Brothers were eventually sold to Edward VI and became part of the Crown Jewels of England from 1551 to 1643. They were worn prominently by Queen Elizabeth I and King James VI and I. In the early 1640s, Henrietta Maria, wife of Charles I, attempted to sell the jewel to raise funds for the English Civil War, but it is unclear if she succeeded. Its whereabouts after 1645 remain unknown.