沉积赤铁矿和层控黄铁矿、菱铁矿的成矿过程中都离不开生物的作用。不同情况下，其表现形式不尽相同。生物的活动形成赤铁矿受层石、毒球状黄铁矿以及有机质的还原作用由赤铁矿转变为菱铁矿。
    冀西北宣龙地区铁质叠层石和铁质核形石同心纹层中普遍含有微体古植物化石，属于低等蓝藻类，形态以丝状体为主，部分为羽状体，它们直接地参与了铁的成矿作用。
   

     Organic action could not be deviated in the minerogenic process of sedimentary hematite,stratabound pyrit and siderite. Its forms of expression are different in different condition.
    Organic activities could form hematite stromatolite and framboid pyrite,and the reduction of organism could transform hematite into siderite.
    In the ferruginous stromatolite and concentric laminae of ferruginous oncolite from the Xuanlong area of Northwest Hebei，there are microplant  fossils in  common. They  belong to rudimentarycyanophyta. Their shags are mainly filamentous and partly pinnate. They directly participated in mineralization of iron.