Observation

This question was attempted by few candidates and their performance was quite poor in (a) part of the question. However, few candidates were able give relevant examples and state the importance of chemically formed sedimentary rocks in the (b) and (c) parts of the question respectively. The answers that were required of the candidates were:

(a)(i) Mode of formation of chemically formed sedimentary rocks

-materials for the formation may be obtained from streams, glacier, winds or organisms

-formed from the accumulation of materials derived from other rocks

-accumulation over a long period of time

-accumulation of these sediments usually under water

-formed through chemical precipitation from rock solutions

-cementation of precipitated rocks

-hardening of cemented rocks

-accumulation of sediments in layers/strata

-variation in thickness of strata

(b) Examples of chemically formed sedimentary rocks

-rock salt

-Nitrates

-Gypsum/calcium sulphate

-dolorite

-dolomite(calcium carbonate)

-potash

-limorite(iron stone)

-limonite

-flint(silicate)

(c) importance of chemically formed sedimentary rocks

-source of minerals

-construction purposes

-as ornaments

-tourist attraction

-soil formation

-raw materials for industries

-food