Often someone will pick a piece up of this beautiful but heavy looking black crystal to buy, at which point I always check with them what it is for. Most times the answer is that it is for 'protection'. When I ask why do they think this, it is usually because they have read about it in a book.
This is a misconception. Schorl has a very dense, heavy and grounding energy. Like most black crystals it can absorb 'negative' and static energies. This 'protection' it gives however, is from such things as mobile phones, Wi-Fi, computers and geopathic stress, with which it deals very happily. If placed near to these with the intent to minimise their emanations, then it will absorb their 'negativity', thus 'protecting' us from them. If someone actually wears or carries around Schorl, rather than protecting their energy field, as it is absorbent, it could instead draw negativity in.
Because it is such a dense and intense energy, it is only used within healing as a very heavy duty grounder, placed beneath the feet of someone who can take its energy (and this is rare). For the majority of people the energy is too potent, and they would be better served by a different, and less intense earthing crystal.
I had a good lesson in just how potent Schorl is whilst teaching a class about its properties a number of years ago. I had placed a large amount of Schorl in the centre of the room so that we could sense its energies collectively. As I began to teach about the crystal I found my mind kept going blank, I couldn't seem to access my own 'higher' knowledge, and I was even having trouble putting my sentences together in a coherent fashion. It took me a few minutes to realise that of course, I had put too much Schorl down in the room. Students remarked it was as if the class was now being conducted from several feet within the earth. It was certainly one way to illustrate its energies!
The crystals which do actually protect and strengthen the energy field are all those with a higher vibration, such as Amethyst, Turquoise, and Lapis Lazuli, which are also therefore safe to use over the whole energy field and chakras. Schorl, in contrast has a very low vibration and is much too dense to place either around the energy field or upon the chakras (with the possible exception of briefly being linked up to the base chakra). If you think of it in terms of the vibrations of colour (the colour of a crystal is part of the reason why it has certain energetic properties, though there are other reasons) it makes sense. The colours violet and purple, deep royal blue and turquoise all vibrate at a fast frequency. Black however vibrates at a very low frequency and what is perceived by the eye as a black object is actually black because it is absorbing all light. Negativity around us also vibrates at lower vibrations, whereas it cannot exist at higher frequencies. However, do please bear in mind that if we have a lesson to learn about something in life, then what we perceive as 'negativity' could still get through, as it is important in some way for our growth.
What I would suggest is, rather than take my word for it, is, if you are already used to wearing or using Schorl about you to protect you then do an experiment. First, just be aware of how you feel and act when you are wearing it, then for three or four days take it off and instead carry some Amethyst or a piece of Turquoise or Lapis with you, with the intent that this protects your energy field. Then afterwards compare your experience of how 'protected' you felt carrying each crystal. I would be very surprised if you did not notice a difference in your moods and general outlook going from using black Tourmaline to one of these other crystals!