Which one of the following materials contains calcium ?

Question

UnlockIAS · Accepted Answer

Correct — C, Gypsum. Gypsum is calcium sulphate dihydrate, CaSO4·2H2O — calcium sits in the formula itself. It is the calcium mineral behind Plaster of Paris (heating gypsum to about 150 °C drives off three-quarters of its water to give the hemihydrate, CaSO4·½H2O) and it is the small percentage of material ground in with cement clinker to slow the setting of Portland cement. Each of the other three options is an aluminium or magnesium mineral with no calcium in it at all.

Why the other options are wrong — (a) China clay is kaolin, whose mineral is kaolinite — a hydrated aluminium silicate, Al2Si2O5(OH)4. It contains aluminium, silicon, oxygen and hydrogen, but no calcium. It is the raw material of porcelain and a coating filler for paper.  (b) Corundum is aluminium oxide, Al2O3 — no calcium. It is Mohs hardness 9 and is used as an abrasive; ruby and sapphire are its gem varieties, coloured by traces of chromium and of iron/titanium respectively.  (d) Talc is a hydrated magnesium silicate, Mg3Si4O10(OH)2 — magnesium, not calcium. It is the softest mineral on the Mohs scale (hardness 1), used for talcum powder and, in massive form, as soapstone.

Concept: This is a straight formula-recall question: identify the cation in each common industrial mineral. Group them by the metal they carry — calcium minerals include gypsum (CaSO4·2H2O), calcite/limestone (CaCO3), fluorite (CaF2), apatite (calcium phosphate) and quicklime (CaO); aluminium minerals include bauxite, corundum (Al2O3) and kaolin; magnesium minerals include talc, magnesite (MgCO3), while dolomite carries both calcium and magnesium.

State PCS 2019 Q17 — Science & Technology PYQ with Answer

State PCS 2019 Q17 — Science & Technology PYQ with Answer