Third, stone skin and muscle. Moist and smooth, feel is good, this also is very important for lingbi stone grade or vice versa.

第三、石肤、石肌。温润、细腻、手感好，这对灵璧石品位高低优劣也极为重要。

youdao

Five see: texture is mainly from the surface of the stone, stone skin to see the hardness of the stone, density and delicate, bright and clean degree.

五看：质地主要是从石头的表层、石肤来看石头的硬度、密度与细腻、光洁的程度。

youdao

Since all forms of potassium alum are soluble in water, when the stone is wet or applied to wet skin, an invisible, fine layer of the mineral is rubbed off the stone and applied to the skins surface.

因为各种状态的钾明矾都能溶于水，当把它弄湿或接触湿皮肤时，会有一层肉眼看不见的细腻矿物层从钾明矾表面脱落，吸附到皮肤表面。

youdao

Each joint was crowned with a little gray stone of skin, and each heel was like the battered end of a club.

NEWYORKER: Naima

Stones that are resistant to lithotripsy may be treated with a surgical procedure known as a percutaneous nephrolithotomy, in which an instrument is passed through the skin into the kidney to grab and break up or remove the stone.

CNN: What can I do for kidney stones?