Both of them generate smoke and ash, most of which is damaging to the inside of tombs. Don't bury, or leave, crystals at the site . I find the most incomprehensible. Most crystals are strip mined from poor countries to supply New Age fads. Many of them do have abilities to carry energy, and therefore are potentially disruptive to the existing energies of the site.
Some people also do things like wedge pennies and other coins into holes in rocks.
These coins will corrode, and as they do they expand, leaking corrosive material over the rocks and lichen. This can cause pressures on the stones themselves, exacerbating any fault or fractures. If removing such offerings, make sure to be careful not to cause more damage in pulling them out of their hidey holes. Berries and seeds should never be put into holes in the stones either, because as they attempt to grow their roots can also exert great stress on any fissures in the rock. Don't leave any remnants of magical work behind you .