In general which of these three cements creates rocks that are the most resistant to weathering?
Iron oxide cement will colour the rock a distinctive rusty yellow-brown as a result of the significant presence of the minerals haematite and limonite. Calcite cement will leave the rock white but is soft, easily scratched by an iron nail and will fizz with the application of dilute hydrochloric acid. Silica cement will leave the rock glassy colourless, glassy white or rarely, a different colour but also glassy, it will resist being scratched by an iron nail, and will not react with dilute hydrochloric acid. The rock with the silica cement will be most resistant to weathering, and will normally remain as a positive relief feature around the surrounding rocks. The cement in the calcite cemented rock will tend to become dissolved away. The iron oxide cemented rock will be fairly soft but will resist erosion better than the rock with the calcite cement.
