Iron oxide concretions are found in sedimentary rocks on both Earth and Mars. On Earth, concretions are common in eolian formations, such as the Jurassic Navajo Sandstone in Utah, USA and those found in the Cretaceous Djadokhta Formation, Gobi Desert, Mongolia. Although it is known that the formation conditions of the iron oxide concretions were affected by the paleoclimate of these regions, quantitative modeling of such formations still requires development, especially concerning initial and diagenetic conditions. A 1-D diffusion–reaction simulation was conducted by assuming that a calcite concretion was initially located in a homogeneous layer of sandgrains. Favorable conditions for the formation of iron oxide concretions have been found to be $4.5⩽\mathrm{pH}⩽6$, and ${10}^{-7}⩽[{\mathrm{Fe}}^{2+}]f_{{\mathrm{O}}_2}⩽{10}^{-5}$, where [${\text{Fe}}^{2+}$] and $f_{{\mathrm{O}}_2}$ are the concentration of ferrous ${\text{Fe}}^{2+}$ ions and dissolved oxygen relative to the atmospheric value, respectively. An iron-rinded concretion from ferric ${\text{Fe}}^{3+}$ ions is not possible. For the case of ${\text{Fe}}^{2+}$ ions, the flow speed of the groundwater should be faster than $2\times {10}^{-5}\mathrm{mm}{\mathrm{s}}^{-1}$. The formation timescale is determined by the diffusion flux of the hydrogen ion, and varies between $2.7\times {10}^2$ and $1.5\times {10}^4$ years for a calcite concretion with an initial radius of 15 mm. Formation conditions of iron-rinded concretions on Earth and Mars are discussed.

在地球和火星的沉积岩中都发现了氧化铁凝结物。在地球上，凝结物在风成岩层中很常见，例如美国犹他州的侏罗纪纳瓦霍砂岩和蒙古戈壁沙漠的白垩纪Djadokhta层中发现的那些。尽管已知氧化铁固结物的形成条件受这些地区的古气候影响，但仍需要开发此类形成物的定量模型，特别是涉及初始条件和成岩条件。一维扩散反应模拟是通过假设方解石凝结物最初位于均匀的沙粒层中而进行的。已经发现形成氧化铁凝结物的有利条件是$4.5⩽\mathrm{pH值}⩽6$和 ${10}^{--7}⩽[{\mathrm{铁}}^{2+}]F_{{\mathrm{Ø}}_2}⩽{10}^{--5}$，其中[${\text{铁}}^{2+}$]和 $F_{{\mathrm{Ø}}_2}$ 是亚铁的浓度 ${\text{铁}}^{2+}$离子和溶解氧相对于大气值。铁的铁结石${\text{铁}}^{3+}$离子是不可能的。对于${\text{铁}}^{2+}$ 离子，地下水的流速应比 $2\times {10}^{--5}\mathrm{毫米}{\mathrm{s}}^{--\mathrm{1个}}$。形成时间尺度由氢离子的扩散通量决定，并且在$2.7\times {10}^2$ 和 $1.5\times {10}^4$方解石凝结的初始半径为15毫米。讨论了地球和火星上铁浸凝结物的形成条件。