准矿物（mineraloid）是指形似矿物但却不具有晶体结构的物质。准矿物都是天然形成的，常常有类似于矿物的外观和色泽，但是其微观结构缺乏有序的原子排列（即晶体结构）。多数时候，准矿物也缺少成为矿物所要求的确定的化学成分。准矿物有时会含有一些通常不被认为是矿物的化学成分，譬如有机物。例如，黑曜石是一种无定形的火山玻璃，而非晶体；煤精是由腐化的木头在极端的压力下变质而成的；蛋白石是由无定形的非晶态二氧化硅所构成；珍珠被一些人认为是矿物，因为它的结构中含有碳酸钙，但是比较科学的分类应将其列入准矿物，因为其晶体是被有机化合物键合而成，并且其缺少固定的成分比例。

A mineraloid is a mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an amorphous glass and not a crystal. Jet is derived from decaying wood under extreme pressure. Opal is another mineraloid because of its non-crystalline nature. Pearl, considered by some to be a mineral because of the presence of calcium carbonate crystals within its structure, would be better considered a mineraloid because the crystals are bonded by an organic material, and there is no definite proportion of the components.