Ores such as siderite, limonite and haematite occur too. Doing so resulted in the formations of magnesite, siderite, and numerous varieties of graphite. The yellow of the false yolk comes from minerals like limonite, siderite, and sulfur. The carbonate siderite is also typically mined. Associated minerals include metavivianite, ludlamite, pyrite, siderite and pyrrhotite. It occurs associated with whitlockite, vivianite, triploidite, triplite, triphylite, siderite, phosphoferrite, fairfieldite and apatite. Magnetometers can also locate zones ignited by lightning and map siderite (an impurity in coal). Greenalite occurs with quartz, stilpnomelane, siderite, chamosite, pyrite and minnesotaite. It is made by phyllites, quartzites, porphyrys and limestones commonly metamorphosed to siderite and magnesite. There are also, more rarely, structures composed of siderite, gypsum, pyrite. Rhodochrosite forms a complete solid solution series with iron carbonate (siderite). They consist of concentric inter-bedded cones of calcite or more rarely gypsum, siderite or pyrite. The crystallographic and physical characters resemble those of dolomite and siderite. In older sediments, the minerals siderite (FeCO), uraninite (UO) and pyrite (FeS) are commonly found. Many gem-quality ammonites are found within siderite concretions.