How Does A Geologist Identify Minerals?

There are thousands of minerals in existence and more are discovered each year. Geologists identify them by analysing their distinctive properties through tests and observations.
Colour is the most readily distinguishing feature of many minerals but it cannot entirely be relied on as an identifier because some minerals can exist in different colours. Hardness is another property of minerals. The German scientist Frederich Mohs developed a scale for classifying the hardness of minerals, now known as the Mohs scale. To assess the hardness of a mineral a geologist would attempt to scratch it with objects of ever increasing hardness. When it becomes scratchable, its hardness is known. The crystalline structure of a mineral is another of its distinctive attributes. What is known as a streak test can also be used. In it, a mineral will be rubbed against a plate of unglazed porcelain, and the colour of the resulting mark, if there is one, can help in identification. Geologists can also measure the specific gravity of a mineral, which is its heaviness compared to the same volume of water, in order to distinguish it from others.
Other attributes which help in identifying minerals are their lustre, their magnetic properties if any, their reaction to acid, their appearance under ultra-violet light, and the distinctive way in which a mineral fractures ~ known as its cleavage.