Theory question 203
Rocks(a) Define the term sedimentary rock and describe any two processes of its formation
(b) Discuss any three ways in which sedimentary rocks are important to man
Show the model answer
(a) Sedimentary rock: rock formed from layers of sediments (rock fragments, plant/animal remains or chemical deposits) laid down in water or on land, then compacted and cemented
Mechanical: weathered fragments transported by rivers, wind, ice and deposited in layers, then compacted (sandstone, shale, conglomerate)
Organic: remains of plants and animals accumulate and harden (coal, limestone, chalk)
Chemical: minerals precipitate from solution when water evaporates (rock salt, gypsum, potash)
(b) Any three: contain fuels (coal, petroleum, natural gas); limestone for cement and lime; sandstone/clay for building, bricks and pottery; rock salt for food and industry; good aquifers for water; form fertile soils
Name a rock example for every process.