Khailon

Long predating humans, the Khailon have endured like stones themselves -- nigh unchanging and content to move on their own geological timescale. The Khailon are one of the galaxy's few known forms of silicon based organic life. They grow from the mineral rich springs of their home planet, an eternal primordial soup that deposits Khailonite -- the living mineral -- over thousands of years. When sufficient Khailonite accumulates, a new Khailon separates from the rock. The Khailon have altered and modified this process, and can now cultivate each generation in carefully controlled accumulation pools.
The Khailon can take countless forms -- there is no one standard biomorphic template for Khailon. Over time, they can stimulate the growth or withering of limbs, adjust the shapes of their bodies, develop new organs, and more. Effectively each Khailon is in its own state of constant, slow evolution. The Khailon's nervous systems are more electrically charged than those of most species, and their long perspective on time makes it difficult for them to interact with non-silicon based life.
Emperor Anatexis Cryslon XI is the cultural master of all Khailon everywhere. While he is called the 11th, this is really the 11th iteration of the same being, which has metamorphosed over the millenia. Each metamorphosis adjusts the emperor's capabilities and demeanour. The current iteration, Anatexis XI, underwent igneous transformation, using fusion forges to deliberately melt part of his anatomy and induce changes. He has adopted an "aggressively isolationist" position. Despite the repeated invitations from the Thaal, the Khailon Empire refuses to join the Galactic Enforcement Agency--but their xenophobia does not extend to one particular species.
The discovery of Humans some three centuries ago precipitated a slow, but enormous, cultural change amongst the Khailon. Humanity's peculiar sexual compatibility extends even to silicon based life. Khailon biology did not include sexual reproduction or any form of sexuality at all, but in the ensuing centuries transformations began to lead them in that direction. It's whispered the reason Emperor Anatexis Cryslon XI underwent igneous transformation was to equip himself with the organs and nervous system functions necessary to experience erotic pleasure, and to interbreed with humans. This is the only exception to his policy of aggressive isolationism. The Emperor has sired multiple half-human, half-Khailon children, most notoriously his daughter Rassilica Crylson III. Khailon hybrids exhibit mammalian characteristics, but their bodies are suffused with crystalline molecules. The introduction of carbon based genetics to Khailon evolution could accelerate the transformation of the species and lead to new discoveries the Khailon people never thought possible.