Crystalline THCA is a product of growing popularity due to its potential to reach extremely high potencies. There’s even been a submitted patent to trademark a particular method for obtaining it.  The basic idea of this product probably came as a result of the technique for making shatter or other full spectrum extracts; it essentially uses the same appliances and materials, but the extract is instead subjected to different conditions to induce crystallization, and we will talk about what those conditions are below.
Ed Rosenthal, author of Beyond Buds, has recently explored these products in a potent online expose. As he points out, Diamond Mining, or Jar Tech, is really a derivative of the basic organic chemistry concept called “Recrystallization”. Applying those techniques to full spectrum extracts, or Live Resin, is the key to learning how to crystallize THC-A, or its decarboxylated and activated derivative, THC.
When growing crystals, there are two concurrent processes that are kept in balance. Growth is the term that defines the rate at which individual crystals that are formed become larger. It depends on how soluble the desired molecule is in the solvent it’s dissolved in, and on the amount of impurities that are in the solution alongside it. Nucleation determines how quickly new crystal “seeds” are formed in the container.
The way to induce crystallization is to lower a mixture below the freezing point of a particular constituent that can then precipitate out of solution as a solid.  The effect that this “undercooling” has on the type of crystals that are formed depends in part on how far below the freezing point the solution is driven down (ΔT), and in part by how fast that cooling temperature is applied and transferred to the solution (ΔT/Δt).
These factors can be thought of as putting a “crystallization pressure” on the dissolved compound, and they affect crystallizations by influencing whether Growth or Nucleation becomes the more important factor. At small to moderate values of (ΔT) and/or (ΔT/Δt), the “pressure” to crystallize can be thought of as being small. The Growth factor dominates Nucleation in the equilibrium that exists between the two, and the conditions favor the formation of few, but large, crystals. When the temperature is dropped either quickly or by a large amount, there is a much stronger drive towards crystallization, and Nucleation becomes much more important in the formation of crystals, leading to many small crystals being formed.
- Dibble, Clare J. and Cole, Isaac B. “Methods for Obtaining Purified Cannabis Extracts and THCA Crystals”. US Patent number US20170008870A1. Accessed May 1, 2019.
- Shea, Thomas and Hammer, Julia E. “Kinetics of cooling- and decompression-induced crystallization in hydrous mafic-intermediate magmas”. J Volcan Geotherm Res. 2013; 260: 127-145 [Times cited = 44, Journal impact factor = 1.483].
Image Credit: Ed Rosenthal.com