Ferroelastic twinning in minerals is a very common phenomenon. The twin laws follow simple symmetry rules and they are observed in minerals, like feldspar, palmierite, leucite, perovskite, and so forth. The major discovery over the last two decades was that the thin areas between the twins yield characteristic physical and chemical properties, but not the twins themselves. Research greatly focusses on these twin walls (or ‘twin boundaries’); therefore, because they possess different crystal structures and generate a large variety of ‘emerging’ properties. Research on wall properties has largely overshadowed research on twin domains. Some wall properties are discussed in this short review, such as their ability for chemical storage, and their structural deformations that generate polarity and piezoelectricity inside the walls, while none of these effects exist in the adjacent domains. Walls contain topological defects, like kinks, and they are strong enough to deform surface regions. These effects have triggered major research initiatives that go well beyond the realm of mineralogy and crystallography. Future work is expected to discover other twin configurations, such as co-elastic twins in quartz and growth twins in other minerals.

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矿物中的铁弹性孪晶：微量元素，电导率和意外压电的来源

矿物中的铁弹性孪晶是非常普遍的现象。孪生定律遵循简单的对称规则，并且在长石，棕铁矿，白榴石，钙钛矿等矿物中观察到。过去二十年来的主要发现是，双胞胎之间的细小区域具有特定的物理和化学性质，但双胞胎本身却没有。研究主要集中在这些双壁（或“双边界”）上。因此，因为它们具有不同的晶体结构并产生各种各样的“新兴”特性。墙体性能的研究大大掩盖了双畴的研究。在这篇简短的评论中讨论了一些壁的特性，例如它们的化学存储能力以及它们在壁内部产生极性和压电性的结构变形，而这些效应在相邻域中都不存在。墙壁包含拓扑缺陷（例如扭结），并且其强度足以使表面区域变形。这些影响引发了重大的研究计划，这些计划远远超出了矿物学和晶体学的范畴。预计未来的工作将发现其他孪晶构造，例如石英中的共弹性孪晶和其他矿物中的生长孪晶。