These crystals come from Boekenhouthoek, North of Pretoria in the Gauteng province of South Africa.
The deep purple ones were called Spirit quartz crystals because the colour was associated with the colour of methylated spirits. Many other colours have been found such a pale purple, ametrine, white, clear and, more recently, bright yellow crystals which are being called Sunshine Quartz crystals.
While they are all still generally referred to a spirit quartz crystals, I feel that cactus quartz is is a better overall term for crystals from this locality