Amethyst

Colors It Comes In - Lilac to purple, reddish-purple and bluish-purple. Its color comes from small amounts of iron and aluminum in its crystal structure. If exposed to heat, amethyst can turn brown, yellow, or green.

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Fracture Pattern -

Rippled fracture: Amethyst can break with a rippled fracture. 
Thumb markings: Amethyst can show "thumb markings". 
Engine turning: The intersection of two sets of curved ripples on a fractured surface can create a pattern similar to "engine turning". 
Brewster fringes: A pattern known as "Brewster fringes" can be seen in natural, twinned amethyst when looking down the optic axis of the gem. 
Phantom crystals: Phantom crystals can be caused by rapid temperature changes that create tiny air bubbles, leaving behind imprints of themselves frozen inside. 

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Shape - It shows classic quartz crystal shape: a six-sided columnar crystal with a pyramid-shaped termination at the top.

 

Luster - Vitreous

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Texture - coarse-grained

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Where It Can Be Found - Amethyst is found in a variety of geologic settings but most commonly as crystals lining cavities or voids in volcanic rock, forming geodes as seen here. The major sources for amethyst are Brazil and Uruguay.

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Hardness On The Mohs Scale - 7 Out Of 10