Obsidian is the heaviest thing you will voluntarily carry out of a cave. At 1.0 weight and 100 per stack, a full stack is 100 weight — the same as crystal, a third of what a metal stack weighs, and fifty times a stack of silica pearls. And it has exactly one job in the cached recipe data: two obsidian per polymer craft.
That single conversion defines the resource. Every number below is a cached field from ark-resources.json.
The obsidian card
| Property | Value |
|---|---|
| Rarity | Uncommon |
| Weight | 1.0 |
| Stack size | 100 |
| Weight of a full stack | 100 |
| Renewable | Yes |
| Refineable | No |
| Combustible | No |
| Hexagon value | not listed |
Obsidian is a rare resource most often found underground and on volcanoes. — ARK Wiki
“No refineable” is the detail that separates obsidian from metal. There is no smelting step, no ingot, no intermediate — it goes from node to Fabricator untouched. That makes the chain shorter and the haul heavier, because you cannot compress it before you carry it.
Two obsidian, one polymer
The polymer entry lists quantity1: 2 against Obsidian. Run that through the weight of both items:
| Polymer made | Obsidian | Obsidian weight | Polymer weight | Compression |
|---|---|---|---|---|
| 1 | 2 | 2.0 | 0.25 | 8x |
| 50 | 100 | 100 | 12.5 | 8x |
| 100 | 200 | 200 | 25 | 8x |
| 250 | 500 | 500 | 62.5 | 8x |
The 8x compression is the reason the Fabricator exists. Obsidian is 1.0 per unit and polymer is 0.25 — the craft turns four units of weight into one, and the only cost is the trip to get the obsidian there.
The 250 row is the one that matters in practice. A Chemistry Bench costs 250 polymer, which is 500 obsidian — five full stacks and 500 weight of cave cargo, before you count the 250 crystal and 250 ingots the bench also wants. That is the real price of the mid-game’s most important structure, and almost none of it is visible from the build menu.
The polymer page covers what happens after the craft, and the crafting guide covers the station that does it.
Obsidian against the other cave resources
Caves hand you several resources at once, and the weight data tells you which to prioritise:
| Resource | Weight | Stack | Weight per stack | Primary use |
|---|---|---|---|---|
| Obsidian | 1.0 | 100 | 100 | Polymer |
| Crystal | 1.0 | 100 | 100 | Stations, C4, lenses |
| Metal | 1.0 | 300 | 300 | Ingots |
| Silica Pearls | 0.02 | 100 | 2.0 | Electronics |
| Rare Mushroom | 0.2 | 100 | 20 | Food, utility |
Obsidian and crystal are identical in weight and stack, which makes the choice between them a pure question of what you need. Metal’s 300 stack is the outlier — a metal slot holds three times what an obsidian slot holds, so metal is the efficient cave cargo and obsidian is the necessary one.
Pearls are the freebies. At 2.0 per stack they cost essentially nothing to add to a cave run, which is why every obsidian trip should come home with electronics feedstock too. The silica pearl page covers the dive.
Where the nodes are, and why the map matters
The infobox says underground, and that is the constraint. Obsidian is a cave-and-peak resource, which means three things:
- You need a light source and a combat plan. Caves are not passive harvesting environments.
- Hauling is the bottleneck. 100 weight per stack means four stacks is already 400 weight — a serious load for anything short of a dedicated carrier.
- The trip should multitask. Crystal, pearls and mushrooms share the same space, so a one-resource cave run is a wasted run.
The Ankylosaurus is the standard harvester for the rock-type nodes, and the Argentavis is the carrier that makes a 400-weight return leg possible. Together they turn a cave from a risk into a route. The gathering guide lists the alternatives.
For map-specific routes, the Aberration guide and Ragnarok guide both cover cave systems where obsidian concentrates, and the exploration guide covers the loadout discipline for going in.
The renewable flag and what it means
Obsidian is marked renewable: Yes, which in ARK terms means nodes respawn rather than that anything farms it for you. There is no obsidian-producing creature and no conversion recipe that manufactures it — the only way to get more is to mine more.
That makes the supply curve simple: your obsidian income is your cave time multiplied by your harvester’s yield. Since the dataset does not publish per-node yields, the useful planning tool is the ratio, not the rate. Each polymer craft needs 2 obsidian, each Chemistry Bench needs 250 polymer, so the bench is 500 obsidian no matter how fast you mine.
The corollary is that obsidian should never be banked in small amounts. Either you are saving for a polymer batch and the obsidian is a project, or you are not and it is dead weight in a chest. The resources strategy page makes the same argument for every heavy material.
A practical obsidian plan
- Mine with polymer in mind. Two obsidian per craft, so count in pairs: 100 obsidian is 50 polymer, which is half a stack of the finished item.
- Convert on site if you can. Polymer weighs a quarter of the obsidian that makes it. A Fabricator at the cave mouth is unrealistic, but crafting before the second trip home is not.
- Fill the light slots first. Pearls at 0.02 and mushrooms at 0.2 cost almost nothing and are the difference between a good cave run and a great one.
- Never haul obsidian for storage. If no recipe is waiting, leave it. It will still be there when the bench is ready.
The resources tier list ranks obsidian against the rest of the set, and the items guide lists the polymer-tier gear it ultimately becomes.