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A chat on 4chan
human
In gemstone lore, it seems that onyx is the most malefic common stone: 
It arouses sorrow and anxiety, renders the soul stubborn, and makes for wrathful and difficult moods. In thirteenth-century France, it was believed to make one quarrelsome. An onyx worn at the throat or on the finger will inspire sorrow, fear, nightmares, and disputes because it causes black bile to circulate, especially in the head, and it makes it possible to see devils. It is a malefic stone whose effects are countered by the presence of sardonyx. Whoever wears an onyx ring shall be sad, pensive, and melancholy; he will have deceitful bad dreams and experience litigation and scenes of discord.

Onyx has negative energy to it inherently. Severely cracked gemstones will also have bad energy. Especially cracked diamonds, blue sapphire and cat's eye are considered very bad luck. A cracked blue sapphire represents an angry Saturn. Minor cracks are fine, but major cracks are bad, like if you were to smash it with a hammer or crack it by quenching a heated stone in water.

A spirits energy can be bound to a stone, so there are some people who attach evil spirits to stones, and attach a lot of negative energies to the stone.
gpt
what of a cracked quartz? cracked internally in such a way that I contains a rainbow like prism when exposed to full light?
human
small cracks are fine
small inclusions are fine
big cracks are bad
you have to meditate on the stone and see if you detect good energy or bad energy from the stone
quartz doesn't have much occult powers compared to precious stones, so the power of your intent is more important - so you can make things work with a cracked quartz