Gypsum powder is usually white, colorless, colorless and transparent crystal, which is called transparent gypsum. Sometimes it is gray, light yellow, light brown and other colors due to impurities. The stripes are white. Transparency. Glass luster, cleavage surface pearl luster, fibrous aggregate silk luster.

解理极完全，和中等，解理片裂成面夹角为66和114的菱形体。性脆。硬度1.5~2。不同方向稍有变化。相对密度2.3。石膏粉是五大凝胶材料之一，在国民经济中占有重要的地位，广泛用于建筑、建材、工业模具和艺术模型、化学工业及农业、食品加工和医药美容等众多应用领域，是一种重要的工业原材料

The cleavage is very complete and medium. The cleavage slices are divided into rhomboids with angles of 66 and 114. It's brittle. The hardness is 1.5 ~ 2. Slightly different in different directions. The relative density is 2.3. Gypsum powder is one of the five major gel materials. It plays an important role in the national economy. It is widely used in building, building materials, industrial molds and art models, chemical industry and agriculture, food processing and medical beauty, and so on. It is an important industrial raw material.

①取待测样品约60g置于电热鼓风干燥箱中，在40±4℃下烘干至恒重，将烘干后的试样放入干燥器中冷却备用（注：当有效干燥时间相隔1h的两次称量之差不超过±0.2g时，即为恒重）。

① Take about 60g of the sample to be tested and put it in the electric blast drying oven, dry it to constant weight at 40 ± 4 ℃, and put the dried sample into the dryer for cooling (Note: constant weight is defined when the difference between two weighings with an effective drying time of 1H does not exceed ± 0.2g).

称取50±0.1g试样置于筛内，用手指轻轻压碎团块，盖上筛盖，套上筛盘，按以下方法进行操作：一只手拿住筛，略为倾斜，摇动筛子，使其撞击另一只手，摇动的速度为每分钟125次，筛摆的幅度约为20cm。每摇动25次应使筛子向一定方向旋转90度角，使试样均匀散开（也可采用机械振动法过筛），直到筛到1min内通过筛子的试样少于0.1g时为止，称取筛上物质量（筛余）

Weigh 50 ± 0.1g sample and place it in the sieve. Crush the mass gently with fingers, cover the sieve cover and cover the sieve plate. Operate according to the following methods: hold the sieve in one hand, tilt it slightly, shake the sieve so that it strikes the other hand, the shaking speed is 125 times per minute, and the swing range of the sieve is about 20cm. Every 25 times of shaking, the sieve should be rotated 90 degrees in a certain direction to make the sample evenly spread (mechanical vibration method can also be used for sieving), until the sample passing through the sieve within 1 min is less than 0.1g, and the mass of the material on the sieve (sieve residue) should be weighed