HOW TO CLASSIFY ROCKS ON SITE? (GEOLOGICAL OR LITHOLOGICAL CLASSIFICATION)

Rocks can be classified on site, on the basis of its physical appearance. By making a through visual inspection we can ascertain the engineering properties of rocks. Field classification of rocks gives us logical insight about the suitability of rocks for engineering purpose. This type of classification is known as geological or lithological classification of rock.

在视觉上检查岩石的同时，我们必须描述岩石的以下属性，例如

• Texture
• Structure
• Composition
• Colour
• Grain size

Let’s know how to describe the above properties of rock

Geological or Lithological Classification of Rock

1.Texture

Rock material may be of any of the following textural groups.

Crystalline

• This type of rocks are composed of visible interlocking crystals or crystal grains
• When scratched by the knife, particles do not come out of the rock mass.

Indurated

• 肉眼不可见互锁晶粒或晶粒。
• Rocks consist of fine grained material
• Particles do not come out of the rock mass when scratched by the knife.

结晶 - 浑浊

• Individual crystal grains or crystal aggregates are finer than crystalline structure but coarser than indurated structure.
• Grains do not come out when scratched by knife

Compact

• Particles or grains are tightly packed
• Grains are finer
• 被刀子划伤的粒子或粉末出来的岩石质量

胶泥

• 谷物是可见的by naked eye
• Size of grains ranges from medium to coarse grained structure
• Particles come out from the rock mass even when scratched with finger nail.

2.Structure

Structure of a rock mass means the orientation of mineral grains within the rock mass. The various types of structures are as follows.

Homogeneous

If the grains and crystals are having random orientation, the structure will be called homogeneous.

Lineated

If mineral particles are having a preferred orientation in a particular linear direction/directions, then the structure will be known as lineated.

Intact-Foliated

When the minerals in the rock mass are having a preferred orientation of a planner nature

Fracture-Foliated

当刨床结构具有闭合或初始断裂时，例如床上用品或切割平面

3.Composition

Rock’s mechanical and physical characteristics are greatly influenced by the presence of calcite. Therefore based one presence of calcite the rock may be classified as follows.

Non calcareous

Non calcareous rock materials are those in which calcium carbonate is absent.

Part calcareous

The rock contains mainly non calcareous material. The calcareous material is present as a bond between grains.

Calcareous

The rock material which are mainly composed of calcite

4.Colour

Light colour

• 岩石本质上是酸性的
• Rocks are generally feldspathic
• Pure calcareous rocks are light in colour

Dark colour

• Rocks are not acidic in nature
• Rocks generally contain ferromagnesium mineral
• Part calcareous rocks are dark in colour.

5.晶粒尺寸

有时岩石的分类是基于它们的粒度完成的。在这种情况下，岩石的来源或类型不是那么重要。基于晶粒尺寸，岩石材料分为3组，如下所述。

Coarse grained

When size of particles or grains are larger than 2 mm

中等颗粒

When size of particle or grain lies between 2 mm to 0.1 mm

Fine grained

When particles are less than 0.1 mm in size and individual grains are invisible to the naked eye