Haematite in the context of "Hexagonal crystal family"

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⭐ Core Definition: Haematite

Hematite (/ˈhiːməˌtaɪt, ˈhɛmə-/), also spelled as haematite, is a common iron oxide compound with the formula Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of Fe
2O
3. It has the same crystal structure as corundum (Al
2O
3) and ilmenite (FeTiO
3). With this crystal structure geometry it forms a complete solid solution at temperatures above 950 °C (1,740 °F).

Hematite occurs naturally in black to steel or silver-gray, brown to reddish-brown, or red colors. It is mined as an important ore mineral of iron. It is electrically conductive. Hematite varieties include kidney ore, martite (pseudomorphs after magnetite), iron rose and specularite (specular hematite). While these forms vary, they all have a rust-red streak. Hematite is not only harder than pure iron, but also much more brittle. The term kidney ore may be broadly used to describe botryoidal, mammillary, or reniform hematite. Maghemite is a polymorph of hematite (γ-Fe
2O
3) with the same chemical formula, but with a spinel structure like magnetite.

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Haematite in the context of Biotite

Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula K(Mg,Fe)3AlSi3O10(F,OH)2. It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous end-members include siderophyllite and eastonite. Biotite was regarded as a mineral species by the International Mineralogical Association until 1998, when its status was changed to a mineral group. The term biotite is still used to describe unanalysed dark micas in the field. Biotite was named by J.F.L. Hausmann in 1847 in honor of the French physicist Jean-Baptiste Biot, who performed early research into the many optical properties of mica.

Members of the biotite group are sheet silicates. Iron, magnesium, aluminium, silicon, oxygen, and hydrogen form sheets that are weakly bound together by potassium ions. The term "iron mica" is sometimes used for iron-rich biotite, but the term also refers to a flaky micaceous form of haematite, and the field term Lepidomelane for unanalysed iron-rich Biotite avoids this ambiguity. Biotite is also sometimes called "black mica" as opposed to "white mica" (muscovite) – both may form in the same rocks, and in some instances side by side.

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LINKED FROM (PARENTS)
← Biotite
LINKS TO (CHILDREN)
American and British English spelling differences → Iron oxide → Iron(III) oxide → Rock (geology) → Soil → Hexagonal crystal family → Iron(III) oxide → Crystal structure → Corundum → Ilmenite → Solid solution → Mining → Iron ore → Pseudomorph → Magnetite → Specular reflection → Streak (mineralogy) → Mohs scale of mineral hardness → Brittleness → Crystal habit → Maghemite → Spinel structure →