Fortunately, every mineral in the world has a unique structure and composition. Because the atomic characteristics are unique, the external physical properties of each mineral will also be unique. Therefore any mineral can be recognized on the basis of the combination of physical properties which it exhibits. These properties can be readily determined with a few simple tests. They include: 

Hardness Hardness is determined by a mineral's resistance to scratching. The hardest mineral in the world is diamond. This does not mean that a one carat stone cannot be shattered by a hammer blow. What it does mean is that diamond will scratch all other minerals. On the other end of the hardness scale lie such minerals as graphite and talc. They can be scratched by all minerals with a hardness greater than their own, i.e., by virtually all other minerals. 

In the last century, an Austrian mineralogist named Mohs set up a numerical scale of hardness ranging from a low of 1 (talc) to a high of 10 (diamond), a scale still used today. Testing to establish the numerical hardness value of a mineral is carried out by comparative scratch tests using minerals of known hardness. In fieldwork, however, hardness is broken into three ranges rather than ten, using commonly available substances such as glass (H=5.5) and fingernails (H=2.5). 

Cleavage, parting, and fracture. All three of these properties relate to the way in which a mineral breaks; therefore they reflect patterns of internal structure. If a mineral exhibits cleavage, it breaks along flat, smooth, parallel, light reflecting surfaces. Parting has intermediate characteristics, in that the break is non-random but it is neither as smooth or light reflecting as in cleavage. In fracture, the break is random. In addition to the type of break, it is also important to note, especially in the case of cleavage, the number of cleavage directions, and the angles at which they intersect. 

Color and streak. Color refers to the color of the whole specimen, whereas streak refers to the color of the powdered mineral. 

Luster. Luster is the sheen of the mineral. There are two basic categories of luster, metallic and non-metallic. Metallic luster gives the mineral the outward appearance of a metal, reflecting light off its surface from all directions. Non-metallic luster 

Crystal form. Because all minerals have a regular arrangement of their molecules, they often exhibit distinct external crystal shapes. When present, this characteristic is often a powerful diagnostic tool. 

Feel. Some minerals may feel smooth to the touch while others do not. 

In addition to the major properties listed above, there are many minor simple tests which can be most helpful, such as taste, smell, heft (whether it feels heavy or not), radioactivity, fluorescence, phosphorescence, etc. In fact, any characteristic which is diagnostic can be, and is used to figure out what mineral a particular specimen is.