Natural Vitality Plant-Sourced Minerals - is a mineral liquid concentrate. It has a very watery consistency. Although I haven't tried it, if you do not have plant-sourced minerals on hand, it could likely be replaced with apple juice.
Apple pieces - float to the bottom of the cupcakes which we loved! If you don't have apples, they're not 100% required for this recipe. If you want to omit them, go for it! You could replace it with ½ teaspoon of vanilla extract.