Some examples of minerals in iron-rich rocks containing oxides are limonite, hematite, and magnetite. It occurs as a secondary phase in oxidized magnetite and limonite deposits. Associated minerals are quartz, limonite, azurite, malachite, cuprite, and other secondary copper minerals. Roasting the limonite changed it partially to hematite, producing red ochres, burnt umbers and siennas. However, there are limonite pseudomorphs after other minerals such as pyrite. Mineral sources such as limestone, chalcopyrite, limonite, and marble are common in the district. Other associated minerals include wulfenite, limonite, and barite. The fossilization process replaced the wood with limonite and hematite. The main minerals mined in Sierra Leone are diamonds, rutile, bauxite, gold, iron and limonite. Ores such as siderite, limonite and haematite occur too. This kind of pigment is known as yellow ochre, yellow earth, limonite, or terra gialla. The same process, at geological speed, results in the gossan limonite ores. Its name is derived from the extensive deposits of limonite (iron ore) once mined here. Absence of the limonite zone in the ore deposits is due to erosion. The ore exploited by the company is the Nickel limonite.