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my question is
1.what the difference between silt and sitystone we identify silt and siltstone in the field

Dear Sir, Goodmorning and Fraternal Greetings!
I am very happy to answer your question to the best of my knowledge and ability.
My answer is as follows

What is difference between Silt and Siltstone:
Silt is another name for clay and is very fine grained. The grain size is from 1/16 to 1/256 of a millimeter in diameter. It is very similar to sandstone in appearance but with a finer texture. Silt is a common sedimentary rock composed of tiny particles smaller that sand size yet larger than clay size (1/16 - 1/256 mm). It is found in stream deposits and lake beds.
Once the silt is deposited, compacted and cemented together it becomes solid stone and  It is called Siltstone. Siltstone is made from silt which is consolidated or compacted silt. This rock may be found as thin beds. Many siltstones contain layers rich in tiny flakes of mica which glitter in the sun. The mica is concentrated along the bedding planes where the rocks break easily.
Silica, calcite, and iron oxides are the most common cementing minerals for siltstone. These minerals are deposited in the spaces between the silt grains by water. Over the course of thousands or even millions of years the minerals fill up all of the spaces resulting in solid rock.

How to identify in the Field?
Silt stone is hardened sedimentary rock that is composed primarily of angular silt-sized particles (0.0039 to 0.063 mm in diameter) and is not laminated or easily split into thin layers. Siltstones, which are hard and durable, occur in thin layers rarely thick enough to be classified as formations.
Siltstones are intermediate between sandstones and shales but are not so common as either. They contain less alumina, potash, and water than shales but more silica; in addition to mica, they may contain abundant chlorite and other micaceous clay minerals. Although many shales contain more than 50 percent silt, not all are siltstones; siltstones differ from these shales in that they commonly are chemically cemented and show such features as cross-bedding (i.e., lamination inclined to the main bedding plane), cut-and-fill structures, and flowage within a layer. Siltstones differ significantly from sandstones due to their smaller pores and higher propensity for containing a significant clay fraction. Although often mistaken as a shale, siltstone lacks the fissility and laminations which are typical of shale. Unless the siltstone is fairly shaly, stratification is likely to be obscure and it tends to weather at oblique angles unrelated to bedding. Siltstone is differentiated by having majority silt, not clay.

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Dr D S Subrahmanyam


All questions related to Geology, Geotechnical Engineering (especially in-situ stress, in-situ Deformability and Shear investigations) required for underground tunnels and excavations, Dimensional Stone Mining. Can't answer Soil dynamics related to Geotechnical Engineering


Geology and Geotechnical Engineering and Dimensional Stone Mining

National Institute of Rock Mechanics (Govt of India)

International Journal of Mining Engineering and some other Indian journals

Doctorate in Geology

Awards and Honors
Reviewer for 3 International Journals

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