xenomorphic
That does not have its characteristic crystalline form but has a form impressed on it by surrounding grains; anhedral.
xenomorphic: a crystal shaped by its neighbors, not itself
In the rock and ore examination work, a xenomorphic crystal is one that lacks its natural geometric form. Instead of developing the clean faces and edges that define a mineral species, the crystal has been squeezed and distorted into the shapes left by adjacent grains during cooling or deformation. The term comes from Greek: xeno (foreign) and morphe (form). What you see is not the mineral's preference, but a record of crowding.
This happens commonly in coarse igneous rocks and in ores that have recrystallized under pressure. When molten material cools slowly, early crystals grow freely and develop their own faces. Later crystals must fill the gaps, forcing them into irregular shapes. In metamorphic rocks, heat and stress squeeze minerals into the available pore space, erasing original crystal boundaries. A xenomorphic feldspar or quartz grain will show curved or sutured contacts where it meets its neighbors rather than flat cleavage planes.
The opposite condition is euhedral, where a crystal has grown freely and displays its full, characteristic shape. Between these extremes sits subhedral: a crystal with some faces visible but others worn flat by contact. These three grades, euhedral to subhedral to xenomorphic, tell you something about cooling rate, space, and stress history. A thin section of granite or a polished ore sample examined under the microscope will show all three types side by side.
Identifying xenomorphic grains matters when you are logging drill core or describing ore textures. A xenomorphic crystal is still identifiable by its internal structure, color, and hardness, but its outline alone will mislead you. In sulfide ores, galena or pyrite often appear xenomorphic where they have been forced between harder silicate grains. In igneous intrusions, xenomorphic quartz filling the spaces between euhedral feldspars is normal and expected.
The term also signals something about the mechanical history of the rock. Xenomorphic textures in an otherwise coarse, crystalline ore body suggest post-crystallization deformation or a crowded cooling environment. That distinction can matter when you are predicting ore behavior during crushing or considering the likely depth of origin of the intrusion.