Peridot

Peridot displays fair toughness due to its natural cleavage planes, which are inherent weak areas in its crystal structure. Daily impacts can cause peridot to fracture easily along these planes.

Peridot is stable for daily use as it resists most environmental factors well. It only shows sensitivity under extreme heat and harsh chemical exposure, which are less common in everyday situations.

Two polymorphs of forsterite are known: wadsleyite (also orthorhombic) and ringwoodite (isometric). Both are mainly known from meteorites.

Peridot is the gemstone variety of forsterite olivine.

Each oxygen atom is bonded to the silicon by a single covalent bond. The four oxygen atoms have a partial negative charge because of the covalent bond with silicon. Therefore, oxygen atoms need to stay far from each other in order to reduce the repulsive force between them. The best geometry to reduce the repulsion is a tetrahedral shape. The cations occupy two different octahedral sites which are M1 and M2 and form ionic bonds with the silicate anions. M1 and M2 are slightly different. M2 site is larger and more regular than M1 as shown in Fig. 1. The packing in forsterite structure is dense. The space group of this structure is Pbnm and the point group is 2/m 2/m 2/m which is an orthorhombic crystal structure.

One of the important factors that can increase the portion of forsterite in the olivine solid solution is the ratio of iron(II) ions to iron(III) ions in the magma. As the iron(II) ions oxidize and become iron(III) ions, iron(III) ions cannot form olivine because of their 3+ charge. The occurrence of forsterite due to the oxidation of iron was observed in the Stromboli volcano in Italy. As the volcano fractured, gases and volatiles escaped from the magma chamber. The crystallization temperature of the magma increased as the gases escaped. Because iron(II) ions were oxidized in the Stromboli magma, little iron(II) was available to form Fe-rich olivine (fayalite). Hence, the crystallizing olivine was Mg-rich, and igneous rocks rich in forsterite were formed.

At high pressure, forsterite undergoes a phase transition into wadsleyite; under the conditions prevailing in the Earth's upper mantle, this transformation would occur at pressures of ca. 14–15 GPa. In high-pressure experiments, the transformation may be delayed so that forsterite can remain metastable at pressures up to almost 50 GPa.

Pure forsterite is composed of magnesium, oxygen and silicon.

Peridot is a mineral that is highly valued in its gemstone form, which is called peridot. But there are no current industrial or commercial uses.

Forsterite was first described in 1824 for an occurrence at Mount Somma, Vesuvius, Italy.

Forsterite-rich olivine is the most abundant mineral in the mantle above a depth of about 400 km (250 mi); pyroxenes are also important minerals in this upper part of the mantle. Although pure forsterite does not occur in igneous rocks, dunite often contains olivine with forsterite contents at least as Mg-rich as Fo₉₂

(92% forsterite – 8% fayalite); common peridotite contains olivine typically at least as Mg-rich as Fo₈₈

. Due to its high melting point, olivine crystals are the first minerals to precipitate from a magmatic melt in a cumulate process, often with orthopyroxenes. Forsterite-rich olivine is a common crystallization product of mantle-derived magma. Olivine in mafic and ultramafic rocks typically is rich in the forsterite end-member.

Forsterite also occurs in dolomitic marble which results from the metamorphism of high magnesium limestones and dolomites. Nearly pure forsterite occurs in some metamorphosed serpentinites. Fayalite-rich olivine is much less common. Nearly pure fayalite is a minor constituent in some granite-like rocks, and it is a major constituent of some metamorphic banded iron formations.

It was named by Armand Lévy in 1824 after the English naturalist and mineral collector Adolarius Jacob Forster.

You won't reach your wit's end with peridot, as it's said to strengthen patience. It's believed that peridot will help you remain calm due to its pacifying effect on your energy. It is supposedly a stone of productivity, giving you the motivation to complete all that's needed of you, maybe even more!