Alchemy is one of two Origins which are closely related to the Mana Origin - the other being Runes, to which Alchemy is also related.   Like Runes, Alchemy can be used by someone who lacks the ability to access Mana directly, if that person has some degree of Magical Talent. 
Alchemy makes use of the innate magical qualities of certain alchemical materials.  These innate magical qualities are based on something known as "Potential Omnessence."  Potential Omnessence differs from other sources of Omnessence in that it is oriented toward, and can only be used for, specific Configurations of Archetypes and Dominions (or in rare cases, any use of a specific Archetype or Dominion).
Each Alchemical substance has three forms:  the raw, or "Natural" form, the extracted, or "Alchemical" form, and the distilled, or "Mystical" form.
For example, consider the Geozan herb "woundwort."  Woundwort is obtained from the roots of the woundwort plant, a small flowering shrub which grows in temperate regions in magically sensitive areas (areas of high Mana Availability) - especially in areas which are still inhabited by the Fae.  Woundwort is useful in brewing a tea which can greatly aid in healing wounds (hence the name).  Shavings from the inner core of the root are the most effective, but shavings from the outer root can also aid in healing.  Alchemists know of this power, and use it in brewing healing potions which are even more effective in healing, because they utilize not only the "natural" magical healing qualities of the herb, but also draw upon the Potential Omnessence of the herb (usually in combination with other alchemical/herbal ingredients) to further enhance the healing effect.
The natural healing qualities of woundwort tea derive from that same Potential Omnessence.  Anyone who brews a good woundwort tea will have a drink which can aid someone in healing or recovering from certain diseases.   But an Alchemist, by extracting or refining the herb into its Alchemical form, can now use his Magical Talent and projection of Will to draw upon that Potential Omnessence directly, using it to shape a Paradigm effect of healing.
Unlike other sources of Omnessence, such Potential Omnessence cannot be used for general effects - to lift a rock, for example, or divine the presence of water underground.  It is only useful for a specific Configuration (in this case, Transformation/Organic), and is most useful for a specific effect (healing).
Further refinement or distillation of the Alchemical substance results in the Mystical form of the substance.  This rarified form is difficult to obtain, but possesses even more powerful properties than the Alchemical form, allowing the Alchemist to create Permanent effects.  The Mystical form of some materials is used in Alchemical Enchanting.
Alchemy requires proper equipment to perform the refining, extracting, or distilling of the substances, and the time to do so.  Accessing Alchemical Potential Omnessence includes the process of extracting or refining necessary to obtain the Alchemical form of the substance.  Further preparation will be necessary to create a specific alchemical effect, once the materials have been refined to the necessary form (Alchemical or Mystical) through Alchemical Processing.
All Alchemical effects are "stored" effects - i.e. the effect is not instantly activated, but is stored in a substantive form (which can vary greatly depending on the forms of the substances used, and the method of activation).  As such, most Alchemical effects are Imbedded or Delayed effects, and the associated costs must be paid.   For example, a potion which must be used within two days would be a Delayed effect, while a protective charm which can only be used once would be an Imbedded effect.   Only effects that will be used in the laboratory itself (usually by the Alchemist) might be able to avoid using  the Delay or Imbed Temper Aspects
Alchemists need at least two skills in addition to their Omnessence skills (Archetypes and Dominions).  Alchemy Lore functions as an Arcane Lore, limiting the Alchemist's effective Configuration Expertise, and serving as a general measure of Alchemical ability.  Alchemists also use Alchemy Lore to research better Alchemical techniques and effects.   Additionally, Alchemists must use Craft: Alchemy in preparing and shaping Alchemical substances.  This represents the Alchemist's aptitude with performing the various physical actions and processes that are necessary in Alchemy.  Additional crafting skills may sometimes be necessary for certain material processes or preparation techniques.
Magical Talent is not strictly necessary to Access or refine Alchemical substances - anyone with Alchemy Lore and Craft: Alchemy can refine / extract the Alchemical form of a substance.  Shaping that substance to create an effect, however, does require Magical Talent.  Some cities may have "alchemists" or "herbalists" with no magical talent whatsoever, who perform the valuable function of gathering and processing Alchemical materials for the use of others, or who utilize those substances in their Natural forms.  The Alchemical form of a substance is generally worth five to twenty times as much as the Natural form, and the Mystical form of a substance can be worth up to one hundred times as much as the Alchemical form.
Note:  some Alchemists consider themselves to be "Herbalists."  This should not be confused with common herbalism (Herb Lore and Healing, Craft: Cooking, or Craft: Brewing, for example), which utilizes only the natural properties of various herbs, such as woundwort.  Any use of the Potential Omnessence of Alchemical substances, herbal or otherwise, is considered Alchemy within the Geoza system.  What the practitioner calls it is up to her.

 

Significant Developments in Alchemy

The first Alchemical use of Potential Omnessence is generally attributed to the Aezjareans.  The discovery of Potential Omnessence proved to be a catalyst for other magical developments, including Mana Imbedding and Delay Temper Aspects.