Just looking at a picture isn’t an accurate way to identify a crystal or mineral. There are times we can identify based on color and shape but to be more certain, it is recommended to learn how to do some mineral identification techniques.
Some things to consider:
Color - Color is something to look at, however is not the best method for identification. There are so many green crystals, for example and just looking at a tumbled green stone, it could be jade, green aventurine, serpentine, and many others.
The streak test – The streak of a mineral is the color of the powdered mineral. The color may include: white/colorless, green, gray/black, red/orange, gold/brown, blue. Most light colored, non-metallic minerals have a white or colorless streak, as do most silicates, carbonates, and most transparent minerals. The streak test is most useful for identifying dark colored minerals, especially metals.
For minerals that are harder than the streak plate, this test cannot be used, since the mineral will remove tile material. A streak plate is about 7 on the Mohs scale. The test is usually performed by scraping the mineral across a piece of unglazed porcelain underside of a ceramic tile.
MOHS Hardness - Friedrich Mohs, a German mineralogist, developed a hardness scale in 1812. This was created to assist with the identification of minerals and ranges 1 being the softest (Talc) to 10 being the hardest (Diamond).
The scale is as follows:
Magnetisim - Some minerals are magnetic such as Magnetite.See if your mystery mineral is magnetic by placing a magnet next to it.
Acid Test - Some minerals contain carbon and oxygen and will have a fizzing action when vinegar or HCL is applied. HCL is hydrochloric acid. and should be handled with care. If you do not have HCL, then try vinegar. I recommend trying vinegar first anyway. Drop one or two drops of vinegar onto your mystery mineral and look for any fizzing reaction. Please note that the vinegar is a mild acid and the fizz action isn't as prominent as it would be with HCL. I use a magnifying glass and good lighting to look for the fizzing. It's also important to note that this test works best with a rough speciman. If there is no fizz, then try HCL. Any fizzing action will tell you that your mineral is a carbonate. I use this test ot help identify Calcite. Other possibilities include: Aragonite, Dolomite, Azurite, Magnesite, Rhodocrosite and others.
Other Things to Consider
Glassy, metalic, dull, shiny, glassy, soapy/greasy, transparency, fluorescence
Location of where the mineral was mined
Most crystal folks really have no interest in mineral identification techniques. I totally understand that! But it is important to have some knowledge, especially when purchasing crystals and minerals. A great tip is to research. Look up: How to identify......(and fill in the blank). For example, "How to identify Jade". You will find wonderful articles with tips. A great resource for the physical characteristics of crystals and minerals (hardness, streak, chemical composition, etc.) is http://www.mindat.org/