Cut the watermelon in quarters. Keep in mind that you will only need about 8 cups of watermelon chunks, so you may not need to use your entire watermelon. Cut the flesh from the rind, then chop into 1 inch pieces. While chopping, be wary of any rouge black seeds. If you see one, pick it out and discard. Measure 8 cups (about 3 pounds) of watermelon chunks and set aside.

Add half of your watermelon, pomegranate juice, raspberries and mint to a blender. Blend until smooth, then transfer to a large bowl (preferably metal). Repeat this process with remaining watermelon, pomegranate juice, raspberries and mint.

Add lime juice and sugar to the watermelon-raspberry mixture, stirring to dissolve the sugar. Taste the granita base to check the balance of sweet and tart. If you find it is too tart, stir in more sugar. If you find it is too sweet, stir in more lime juice.

Cover the bowl with plastic wrap and freeze mixture for 2 hours. Take the bowl out of the freezer and scrape the icy bits from the edges to the center.

Repeat this scraping process every 30 minutes until the entire mixture is frozen and flaky.