贺兰山小口子是贺兰石砚材的故乡,因此而得其名。它是一种浅绿色花斑(俗称“绿彩”)的紫红色基质(俗称“紫底”)的粉砂质泥质板岩。产于贺兰山“长城系黄旗口群”的底部,成为石英岩中的一个夹层。它在小口子厚十多米,延长数百米。层位稳定,但相变明显。沿走向砂质增高,可渐变为砂质板岩。其实,这个层位在贺兰山中,北段的大口子、黄旗口、王金口等地皆有出露,只是随着砂质增多,结构变粗,而失去工艺价值。唯小口子一处得天独厚,是质地细密、结构均匀、清雅莹润、绿紫相依、坚而可雕、刚柔相宜的砚材。其原因何在?原来,早在长城纪早期,小口子正值贺兰海槽的西北端,是一个较 Helan Mountain small hole is the hometown of Helan Stone Inkstone, hence its name. It is a silvery argillaceous slate with a light green patchy (commonly known as “green”) mauve base (commonly known as “purple base”). Produced in the Helan Mountain “Great Wall Department of Yellow Qikou group ” bottom, a quartzite in the mezzanine. It is more than ten meters in the little hole, extending a few hundred meters. The horizon is stable, but the phase change is obvious. Sandy along the higher, can be changed to sandy slate. In fact, this layer in the Helan Mountain, the northern section of the Big Kouzi, Huangqi mouth, Wang Jinkou and other places are exposed, but as the sand increased, the structure becomes thick, and lost the value of the craft. Only a small hole a blessed, is the texture of fine, uniform structure, elegant Yingrun, green purple dependent, firm and carved, rigid affordable affordable material. The reason why? Originally, as early as the Great Wall in the early years, a small hole in the northwestern Helan Trough, is a more