The earth's crust consists of many rocks and minerals. Some of them were formed relatively recently, others - several billion years ago. In this article, we will introduce you to one of the oldest rocks on our planet - ferruginous quartzites. What do they look like and what properties do they have? And how are people used? Read about all this below.
General information about the breed
Ferruginous quartzite (other common names are jaspilite, itabirite, taconite) is a metamorphic rock of chemogenic sedimentary origin with a characteristic thin-layered structure. This is the most common in nature, "member" of the iron-siliceous formations.
Ferruginous quartzites include the following minerals:
- quartz;
- magnetite;
- martitis;
- hematite;
- biotite;
- chlorite;
- pyroxene;
- amphibole and others.
The presence of other minerals in the rock can be determined by the composition of the primary sediment, as well as by the depth of the processes of metamorphization.
Deposits of ferruginous quartzites are usually confined to shields and platforms of the Precambrian period. The formation of this rock occurred approximately 2.5-3 billion years ago. For comparison: the age of our planet is estimated by scientists at 4.5 billion years.
The main properties of the breed
Ferruginous quartzites are distinguished by the following set of physical and mechanical characteristics:
- Hardness - 7 points on the Mohs scale.
- The color of the breed is reddish-brown, dark; sometimes gray or red-gray.
- The density of ferruginous quartzites is 3240-4290 kg / m 3.
- Compression strength - from 180 to 370-400 MPa (depending on the content of silicates in the rock).
- Refractoriness - up to +1770 ̊С.
- The structure of the rock is fine-grained or crystalline-grained.
- The texture of the rock is layered, thin-striped.
Ferruginous quartzites: origin and distribution of the rock
Jespilites can occur in beds of various thicknesses in the strata of ancient rocks of metamorphic origin. Often they are combined with mica, amphibolites, schists or gneisses. As a rule, ferruginous quartzites are a product of metamorphization of volcanic-sedimentary rocks significantly enriched in iron oxides. The latter are usually carried out as a result of active volcanic eruptions occurring under water.
The richest deposits of ferruginous quartzites are concentrated on the Kola Peninsula, in Krivorozhye (Ukraine), in the Far East, northern Kazakhstan, in the Upper Lake region (USA), as well as within the Kursk Magnetic Anomaly. The following states own the largest reserves of this mineral resource:
- Russia;
- Ukraine;
- USA;
- Australia;
- India;
- Kazakhstan;
- SOUTH AFRICA;
- Liberia;
- Guinea;
- China.
Varieties of ferruginous quartzites
In petrology, jespilites are distinguished:
- Broad-band (over 10 millimeters).
- Medium-striped (3-10 millimeters).
- Thin-banded (up to 3 millimeters).
Genetic types of ferruginous quartzites:
- Magnetite.
- Hematite.
- Martite.
- Hydrohematite.
- Magnetite-Ankerite.
- Magnetite-hematite with layers of jasper (actually jespilites).
The chemical composition of a particular sample is determined by the content of silicate and ore minerals, as well as the degree of crystallization of the rock. However, a characteristic feature of all ferruginous quartzites is the fact that SiO 2, FeO, and Fe 2 O 3 substances add up to 90% of the total rock mass. The remaining components are present in small proportions (not more than 1-2%).
It is worth noting that the oldest ferruginous quartzites on Earth were discovered on the island of Greenland, in the Isua region. Their age is estimated by geologists at 3, 760 million years.
Stone application
Ferruginous quartzites are widely used in the iron and steel industry as raw materials for the production of metal, cast iron and some other products. In addition, souvenirs and inexpensive jewelry are made from processed and polished jespilites, which have unusual patterns.
Lithotherapists ascribe to Jespilites a unique ability to purify the blood, improve its circulation and save women from acute menstrual cramps. In esoterics, it is generally accepted that this stone has powerful energy. Jesils talismans play the role of a shield for a person, protecting their owner from dark personalities and evil intentions.
Quartzite enrichment in industry
A layer of ferruginous quartzite with a ferrum content of over 30% is called iron ore. However, such ore requires enrichment. This is a set of technical measures, the ultimate goal of which is to increase the percentage of iron in the rock to maximum values. How are these processes implemented?
At the very beginning of the technical cycle, iron ore extracted from a mine or quarry is sent to a crushing plant. Large blocks of rock undergo several stages of crushing there, resulting in fine quartzite powder.
The next stage is the separation of particles of pure iron from the particles of the so-called gangue. For this, quartzite grains are poured together with a stream of water into a magnetic separator. Iron particles are attracted by magnets, and mineral fragments of quartzite are sieved. At the output, a concentrate is obtained, which is then sintered into pellets and sent to a metallurgical plant for subsequent steelmaking.
