Recent measurements from Mars document X-ray amorphous/nano-crystalline materials in multiple locations across the planet. Despite their prevalence, however, little is known about these materials or what their presence implies for the history of Mars. The X-ray amorphous component of the martian soil in Gale crater has an X-ray diffraction pattern that can be fit partially with allophane (approximately Al₂O₃⋅(SiO₂)_1.3–2⋅(H₂O)_2.5–3), and the low-temperature water-release data are consistent with allophane. The chemical data from Gale crater suggest that other silicate materials similar to allophane, such as Fe-substituted allophane (approximately (Fe₂O₃)_0.01–0.5(Al₂O₃)_0.5–0.99⋅(SiO₂)₂⋅3H₂O), may also be present. In order to investigate the properties of these potential poorly crystalline components of the martian soil, Fe-free allophane (Fe:Al = 0), Fe-poor allophane (Fe:Al = 1:99), and Fe-rich allophane (Fe:Al = 1:1) were synthesized and then characterized using electron microscopy and Mars-relevant techniques, including infrared spectroscopy, X-ray diffraction, and evolved gas analysis. Dissolution experiments were performed under acidic (initial pH values pH₀ = 3.01, pH₀ = 5.04), near-neutral (pH₀ = 6.99), and alkaline (pH₀ = 10.4) conditions in order to determine dissolution kinetics and alteration phases for these poorly crystalline materials. Dissolution rates (r_diss), based on the rate of Si release into solution, show that these poorly crystalline materials dissolve approximately an order of magnitude faster than crystalline phases with similar compositions at all pH conditions. For Fe-free allophane, logr_diss = –10.65–0.15 × pH; for Fe-poor allophane, logr_diss = –10.35–0.22 × pH; and for Fe-rich allophane, logr_diss = –11.46–0.042 × pH at 25°C, where r_diss has the units of mol m^–2 s^–1. The formation of incipient phyllosilicate-like phases was detected in Fe-free and Fe-rich allophane reacted in aqueous solutions with pH₀ = 10.4 (steady-state pH ≈ 8). Mars-analog instrument analyses demonstrate that Fe-free allophane, Fe-poor allophane, and Fe-rich allophane are appropriate analogs for silicate phases in the martian amorphous soil component. Therefore, similar materials on Mars must have had limited interaction with liquid water since their formation. Combined with chemical changes expected from weathering, such as phyllosilicate formation, the rapid alteration of these poorly crystalline materials may be a useful tool for evaluating the extent of aqueous alteration in returned samples of martian soils.

最近来自火星的测量记录了地球上多个位置的 X 射线非晶/纳米晶体材料。然而，尽管它们很流行，但人们对这些材料或它们的存在对火星历史的意义知之甚少。盖尔陨石坑中火星土壤的 X 射线无定形成分具有 X 射线衍射图，可以部分拟合水铝石（约 Al ₂ O ₃ ⋅(SiO ₂ ) _1.3-2 ⋅(H ₂ O) _2.5-3 )，低温放水数据与水铝石一致。盖尔陨石坑的化学数据表明，其他类似于水铝石的硅酸盐材料，如铁取代水铝石（约（Fe ₂ O₃ ) _0.01–0.5 (Al ₂ O ₃ ) _0.5–0.99 ⋅(SiO ₂ ) ₂ ⋅3H ₂ O)，也可能存在。为了研究火星土壤中这些潜在的结晶性差的组分的特性，无铁水铝烷 (Fe:Al = 0)、贫铁水铝烷 (Fe:Al = 1:99) 和富铁水铝烷 (Fe :Al = 1:1) 被合成，然后使用电子显微镜和火星相关技术进行表征，包括红外光谱、X 射线衍射和逸出气体分析。在酸性（初始 pH 值 pH ₀  = 3.01，pH ₀  = 5.04）、近中性（pH ₀ = 6.99) 和碱性 (pH ₀  = 10.4) 条件，以确定这些低结晶材料的溶解动力学和改变相。溶解速率 ( r _diss )，基于 Si 释放到溶液中的速率，表明这些结晶性差的材料在所有 pH 条件下的溶解速度比具有相似组成的结晶相快大约一个数量级。对于无 铁水铝烷，log r _diss = –10.65–0.15 × pH；对于贫 铁水铝烷，log r _diss = –10.35–0.22 × pH；对于富 铁水铝烷，log r _diss = –11.46–0.042 × pH at 25°C，其中r _diss的单位为 mol m ^–2 s ^–1。在 pH ₀  = 10.4（稳态 pH ≈ 8）的水溶液中反应的无铁和富铁水铝石中检测到初始页硅酸盐样相的形成。火星模拟仪器分析表明，无铁水铝石、贫铁水铝石和富铁水铝石是火星无定形土壤成分中硅酸盐相的合适类似物。因此，火星上的类似材料自形成以来与液态水的相互作用一定是有限的。结合风化预期产生的化学变化，例如层状硅酸盐的形成，这些结晶性差的材料的快速变化可能是评估返回的火星土壤样品中含水变化程度的有用工具。