一名太乙元精石。又曰阴精石。乃咸卤津液流渗入土。年久结成石片。大者如杏叶
。小者如鱼鳞。悉皆六出。（禀积阴之气象老阴之数）尖角端正如龟甲状。色绿而莹澈。（蒲
解出者。其色青白通澈。蜀中赤盐之液所结者。色稍红光。）叩之则直理而坼。坼处亦六角
。如柳叶大。烧过则悉解坼。片片相离。白如霜雪。平洁可爱。今世所用元精。乃绛州所出
绛石。非元精也。（濒湖）
味甘咸。气温。性降。伏硫黄丹砂。主除风冷邪气。湿痹。心腹积聚冷气。止头痛。合
诸药。治伤寒阴毒证。又治上盛下虚。痰结目障翳。木舌咽喉疮。来复丹。（申铁饔）同硫
黄硝石用。治上盛下虚。救阴助阳。有扶危拯逆之功。凡缓急诸病。但有胃气。服此丹无不
获安。正阳丹。治伤寒三日。头疼壮热。四肢不利。元精石硝石硫黄各二两。 砂二两。细
研。入瓶固济。以炭火半斤。于瓶子周一寸 之。约近半日。候药青紫色。住火。待冷取出。
用腊雪水拌匀。仍入罐子。置屋后北阴下阴干。又入地埋二七日。取出研细。面糊丸。芡实
大。先用热水浴后。以艾汤研下一丸。衣盖取汗瘥。
〔论〕 元精石为积阴之气所结。角皆六出。是老阴也。阴之极然后生阳。此阴阳之元
机。故其用多主归气于肾。以其同于至阴而有阳也。至阴之所归而阳随之。所以除风冷诸气。
而开宝并云益精气也。来复丹治上实下虚。大是妙剂。盖下虚用硫归之。不得至阴。则阳不
还其宅。上实用硝散之。不得至阴之归。则阳不降于下。即入正阳丹治伤寒阴毒。亦同此意。
然则木舌喉疮。何仍用之以疗热乎。曰。此二治俱有寒水石牙硝以去其热矣。其用元精石亦
犹是引阳归阴之义。先哲立方。岂苟然而已。且其气不寒而温。温不与热同。如春温之气继
于冬寒之后。所谓阳之初复。去寒不甚远耳。
Yu Jing Shi (Crystal of Primordial Essence), also known as Tai Yi Yuan Jing Shi (Great Unity Crystal of Primordial Essence) or Yin Jing Shi (Yin Essence Stone). It is formed when saline brine seeps into the soil and crystallizes over many years into stone flakes. The larger ones are like apricot leaves, and the smaller ones like fish scales; all exhibit a hexagonal shape. (This reflects the accumulation of Yin energy, corresponding to the number six of Old Yin.) The sharp angles are upright and regular, resembling turtle shells. The color is green and crystal clear. (Those from Pu Jie have a clear cyan-white color; those formed from the liquid of red salt in Shu have a slightly reddish hue.) When struck, it splits along straight lines with hexagonal cross-sections, about the size of willow leaves. After calcination, it completely disintegrates into separate flakes, white as frost and snow, smooth and clean, pleasing to the eye. What is currently used in the world as "Yuan Jing" is actually Jiang Shi (Jiang Stone) from Jiangzhou, not true Yuan Jing Shi. (Li Shizhen)
It tastes sweet and salty, has a warm temperature nature, and its action is descending. It can subdue Realgar (Realgar, 丹砂) and Sulfur. It primarily treats the expulsion of Wind-Cold pathogenic factors, Bi syndrome (Bi Syndrome, 湿痹) caused by dampness, and cold qi accumulation in the heart and abdomen. It stops headache. When combined with other herbs, it treats Yin Toxicity Syndrome in Cold Damage diseases (Cold Damage Yin Toxicity Syndrome, 伤寒阴毒证). It also treats conditions of Upper Excess and Lower Deficiency (Upper Excess and Lower Deficiency, 上盛下虚), phlegm nodules causing visual obstructions (Visual Obstruction due to Phlegm Nodules, 痰结目障翳), wooden tongue (Wooden Tongue, 木舌), and sores in the throat. Lai Fu Dan (Reviving Return Pill): (Shen Tieyong notes) used together with Sulfur and Niter, it treats Upper Excess and Lower Deficiency, rescuing Yin and assisting Yang, possessing the merit of supporting critical conditions and reversing adverse trends. For any acute or chronic illness, provided there is still Stomach Qi (Stomach Qi, 胃气), taking this pill ensures recovery. Zheng Yang Dan (Correct Yang Pill): Treats Cold Damage after three days, characterized by headache, high fever, and inability to move the limbs. Formula: Yu Jing Shi (Crystal of Primordial Essence), Niter, and Sulfur, each two liang; Nao Sha (Ammonium Chloride, 硇砂), two liang. Grind finely, place in a bottle, seal tightly with mud, and calcine around the bottle using half a jin of charcoal at a distance of one cun for approximately half a shichen. Wait until the medicine turns cyan-purple, then stop heating. After cooling, take out, mix evenly with snow water from winter, put back into a jar, and dry in the shade under the north side of the house. Bury in the ground for fourteen days, take out, grind finely, bind with wheat paste into pills the size of Euryale seeds. First, take a hot bath, then swallow one pill with Mugwort decoction, cover with blankets to induce sweating for cure.
[Discussion] Yu Jing Shi is formed by accumulated Yin Qi, with hexagonal angles, representing Old Yin. Only when Yin reaches its extreme does Yang generate; this is the primordial mechanism of Yin and Yang transformation. Therefore, its therapeutic action mainly guides Qi to return to the Kidney, as it shares the nature of Extreme Yin while containing Yang. Where Extreme Yin returns, Yang follows. Thus, it expels various Cold-Wind pathogens, and Kai Bao Ben Cao (Kai Bao Materia Medica, 开宝本草) states it also benefits Essence and Qi. Lai Fu Dan treats Upper Excess and Lower Deficiency, which is a wonderful prescription. Generally, for Lower Deficiency, Sulfur is used to guide Qi to Extreme Yin; without reaching Extreme Yin, Yang cannot return to its residence. For Upper Excess, Niter is used to dissipate it; without returning to Extreme Yin, Yang cannot descend to the lower part. Even when using Zheng Yang Dan to treat Cold Damage Yin Toxicity, the principle is the same. However, why is it still used to treat heat conditions like Wooden Tongue and Throat Sores? The answer is that both treatments include Han Shui Shi (Calcined Gypsum, 寒水石) and Ya Xiao (Niter) to clear heat. The use of Yu Jing Shi here follows the meaning of guiding Yang to return to Yin. Did the sages formulate prescriptions arbitrarily? Moreover, its nature is not cold but warm; warmth is not the same as heat. It is like the warm air of spring following the cold of winter, representing the initial return of Yang, not far from coldness.