Oliviine

Oliviine is a mineral that is a member of the olivine group. The olivine group consists of silicate minerals with the general formula (Mg, Fe)2SiO4. Oliviine specifically refers to the end-member of the olivine series that is rich in magnesium, with the ideal chemical formula Mg2SiO4. In reality, natural olivine is almost always a solid solution between forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Therefore, oliviine is often used to describe the magnesium-rich portion of this solid solution, where the iron content is relatively low.

This mineral is a common constituent of the Earth's upper mantle, where it forms a significant portion of peridotite. It is also found in mafic and ultramafic igneous rocks that have been crystallized from magma, such as basalt and gabbro. Due to its abundance in the mantle, oliviine is an important mineral for understanding the composition and dynamics of the Earth's interior. Its physical properties, such as its density and melting point, are crucial for geophysical models.

Oliviine typically appears as granular masses within rocks, but can also form distinct crystals. It is usually green in color, with the intensity of the green hue often correlating with the iron content. Higher iron content tends to produce darker green or even brownish colors. Gem-quality olivine is known as peridot and is highly valued for its vibrant green color. Oliviine is relatively hard, with a Mohs hardness of 6.5 to 7, and is moderately dense. It is also susceptible to alteration, especially in the presence of water, where it can transform into serpentine minerals.