Home > Knowledge > Content
Rock Hardness Classification
Oct 08, 2018

Rock hardness classification



Rock level firmness representative rock

I The strongest The strongest, dense, tough quartzite, basalt and a variety of other particularly strong rocks. (f=20) II Very strong Very strong granite, quartz porphyry, siliceous schist, stronger quartzite, the strongest sandstone and limestone. (f=15)

III Rugged Compact granite, strong sandstone and limestone, quartz veins, strong conglomerate, and strong iron ore. (f=10)

IIIa Rugged Strong sandstone, limestone, marble, dolomite, pyrite, and unsturdy granite. (f=8)

IV is relatively strong in general sandstone and iron ore. (f=6)

IVa is relatively solid sandy shale and shale sandstone. (f=5)

V Medium sturdy Solid muddy shale, unsound sandstone and limestone, soft gravel. (f=4)

Va Medium sturdy Various unsturdy shale, dense marl. (f=3)

VI Softer soft shale, soft limestone, chalk, salt rock, gypsum, anthracite, broken sandstone and stony soil. (f=2)

VIa is relatively soft gravel soil, broken shale, bonded gravel, gravel, strong coal, hardened clay. (f=1.5)

VII Soft and soft clay, soft coal, strong impact soil, clay soil. (f=1)

VIIa Soft soft sandy clay, gravel, loess. (f=0.8)

VIII Soil humus, peat, soft sandy soil, wet sand. (f=0.6)

IX Loose sand, gravel piles, fine gravel, loose soil, mined coal. (f=0.5)

X Sandy sand, swamp soil, watery loess and other watery soils. (f=0.3)


In the long-term practice, people realize that some rocks are not easy to break, some are difficult to break, and hard-to-break rocks are difficult to rock, and it is difficult to blast. Their hardness is also relatively large, in general, it is relatively strong. Therefore, people use the concept of rock solidity to indicate the difficulty of rock breaking.

The firmness is expressed by the coefficient of firmness, also known as the hardness factor, also known as the Platt hardness coefficient (f value).

Robustness factor f = R / 100 (R unit Kg / cm2) R-rock standard sample unidirectional ultimate compressive strength value.

Such as:

1 Extremely strong rock f=15~20 (sturdy granite, quartzite, limestone, etc.)

2 solid rock f=8~10 (unstable granite, strong sandstone, etc.)

3 medium solid rock f=4~6 (ordinary sandstone, iron ore, etc.)

4 not strong rock f = 0.8 ~ 3 (such as loess, only 0.3)

The robustness of the rock is also a property against external forces, but its strength with the rock is two different concepts. Strength refers to the unidirectional action of rock, such as compression, tensile, bending and shearing, while the external force resisted by firmness is a comprehensive external force (such as resistance to sputum, sputum, mechanical crushing, and the combined effect of explosives). force). Mohs hardness The scratch hardness commonly used in ceramics and mineral materials is called Mohs hardness. It only indicates the order of hardness from small to large, and does not indicate the degree of hardness. The mineral behind can scratch the surface of the front mineral. Generally, the Mohs hardness is determined by the Mohs hardness scale of the standard of 10, and then the Mohs hardness is divided into 15 grades due to the appearance of some artificially hardened materials.

Vickers Hardness In the study of ceramic materials, the hardness of a material is accurately determined, usually on a Vickers microhardness tester.


Rock grading

Rocks can be divided into three categories:

1. Magmatic rock (spouted rock) 2, sedimentary rock 3, metamorphic rock

1. Magmatic rocks are mainly: granite, andesite, diorite, rhyolite, basalt, gabbro and so on.

2. Sedimentary rocks are mainly composed of quartz sandstone, lime conglomerate, mudstone, dolomite, mudstone and gypsum.

3. Metamorphic rocks mainly include gneiss, chlorite schist, phyllite, marble, and mica schist.

Although the appearance of rocks is ever-changing, from their formation environment, that is, from the genesis, rock can be divided into three categories: sedimentary rocks, magmatic rocks and metamorphic rocks.

1. Sedimentary rocks: Sedimentary rocks are a type of rock formed at a surface or near-surface not too deep. It is transported, deposited and petrochemicalized by weathering products, volcanic substances, organic matter and other debris materials under normal temperature and pressure. The last formed rock. Either way, the debris material is transported, then deposited in a suitable environment, and after a long compaction, it is petrified into hard sedimentary rocks. Sedimentary rocks are divided into conglomerate, sandstone, shale, and limestone according to the size of the sediment particles.

Formation of sedimentary rocks:

1. Weathering erosion: The large stones on the river are eroded by the years and gradually disintegrate into small sediments and debris.

2. Handling: These debris are transported from the upstream to the downstream by the water flow.

3. Stacking: The downstream flow rate is slowed down, the handling force is reduced, and rock debris is deposited.

4. Compaction: The new sediment is pressed against the old sediment. After a long time, the sediment underneath is pressed tightly.

5. Cementation: Groundwater passes through the pores of the sediment, and the minerals are filled to fill the pores, so that the rock debris particles are tightly cemented together to form sedimentary rocks.

6. Exposed: The sedimentary rock layer deposited on the seabed is arched out of the sea surface under the push of the plate movement to expose the surface.

2. Magmatic rock: Magmatic rock, also called igneous rock, is a magma formed in the deep crust or in the upper mantle. It is invaded into the upper part of the earth's crust or ejected from the surface to form a rock that is solidified and crystallized. Because its formation conditions and sedimentary rocks are very different, its characteristics are also significantly different from sedimentary rocks. Magmatic rocks are divided into andesite, basalt and granite. There is underground magma cooling and solidification. Different igneous rocks are formed due to different magma composition and cooling methods.

Formation of magmatic rocks:

1. Andesite: The magma is sprayed from the crater to the ground and formed by rapid cooling.

2. Basalt: The magma flows out through the tempering eruption and gradually forms condensation.

3. Granite: The magma does not spray out of the ground, but is slowly formed in the ground.

3. Metamorphic rocks: During the formation and development of the earth's crust, the previously formed rocks, including sedimentary rocks and magmatic rocks, have undergone mineral composition adjustment, structural structural changes, and even chemistry in the solid state due to subsequent changes in geological environment and physical and chemical conditions. The composition changes to form a new type of rock called a metamorphic rock. Metamorphic rocks are one of the most important rock types in the continental crust. Metamorphic rocks are divided into slate, schist, gneiss, and marble.

Metamorphic rock formation:

1. The rock formation before metamorphism: due to sedimentation or volcanism, a layer of rock formation is accumulated.

2. Extrusion rock formation: Under the action of strong pressure and friction, temperature and pressure are generated, which causes metamorphism in deep underground rock.

3, metamorphism into new rock: the mineral crystals dispersed in the rock will be arranged in a regular manner, or produce new minerals, and become a variety of new metamorphic rocks. On the global land surface, sedimentary rocks cover 75%, and magmatic and metamorphic rocks account for 1/4 of the land area. But in the depths of the ground, sedimentary rocks have gradually become ethnic minorities. In the entire crust, sedimentary rocks account for only 8% of the crust volume, metamorphic rocks account for 27%, and the remaining 65% are magmatic rocks.

Related Industry Knowledge