There are several crystals that are believed to help improve a negative mindset. Here are a few that you may find helpful:

1. Clear Quartz - This crystal is believed to amplify energy and thought, and may help clear negative thoughts and emotions.

2. Amethyst - Amethyst is considered to be a highly spiritual crystal that can help calm the mind, reduce stress, and promote inner peace.

3. Black Tourmaline - This crystal is believed to have protective properties and may help block negative energy from entering the mind.

4. Citrine - Citrine is thought to promote positivity and optimism, and may help boost confidence and self-esteem.

5. Rose Quartz - This crystal is often associated with love and compassion, and may help promote feelings of self-love and self-care.

6. Selenite - Selenite is believed to have purifying properties and may help cleanse the mind of negative energy and thoughts.