Amala-vijñana is the ninth consciousness and it is a consciousness termed "tattva," which is best tranlated as "suchness."
This suchness is the experience, beyond words and the senses related to them, that touches any phenomenon. It is experiencing, not knowing, the true nature of things. In Chinese it is called 眞如 zhēnrú, and the Chinese characters signify "the truth as it is," namely for students of Chan Dharma and Dao, "the uncarved wood."
As such, it is a set of unstained processes of the right hemisphere, and whilst it is one unstained thing it can be divided into three processes: the process of generating "function," the process of generating "essence," and the process of generating "undifferentiated form."
When it is mentioned, texts speak of it having two dimensions, but really they are speaking of "Essence," which actually OBSERVES the operation of the six senses but not their content or other information and is OBSERVING, though not an observer, for it monitors the operation of the sixth sense "thinking" and its operation also without considering content.
It is this OBSERVING that is converted by Alaya in a sense of self-hood and Klista-manas in Identity which is stained.
The ninth consciousness is indestructible while the full consciousness lasts, but it is modified by evolution since as the Mother Principle its major function is survival of the species it serves.
Chan contemplations permit the experiencing of Function, Essence and Undifferentiated Form and it is from these experiences, when dwelt in, that the Awakening to full suchness arrives.