From a spiritual point of view, crystals have been used for centuries for healing. In Feng Shui we can use crystals in home as beautiful decoration items with a specific energy, but it is not a must.
The use of crystals in Feng Shui is part of a modern version of Feng Shui that’s been adapted to make it relevant for the current time. A lot of Feng Shui practitioners do use crystals, I personally also love to use crystals in my Feng Shui practice, but they’re not necessary.
Natural crystals are actually not an integral part of Feng Shui. If we look at any older Feng Shui books, we will not see any crystals, except maybe jade as it was used often in Asia.
In some Feng Shui practices (e.g. BTB) there are Feng Shui crystal balls used. In the BTB tradition, these faceted crystal balls are very important, but they’re also not necessary. There’s always something else you could use as an adjustment instead.
Feng Shui is about shifting the energy in your environment. You can use many different tools, including natural crystals or crystal balls, but they’re not a must. When you work with a consultant, they’ll be able to give you adjustments that are appropriate for you and customized to what you’re working on.