How to Identify Black Locust Wood (Robinia pseudoacacia)

Black Locust, Robinia pseudoacacia: color, grain, end grain, Janka hardness (1,700 lbf) and weight, and how to tell it from Osage Orange, quoted from the USDA Wood Handbook and The Wood Database.

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At a glance

Scientific name: Robinia pseudoacacia
Type: Hardwood
Origin: Eastern United States (Appalachian region, widely naturalized)
Color: Color ranges from pale greenish-yellow to darker brown, darkening to a russet brown with age.
Grain and texture: Grain usually straight, with a medium texture.
End grain: Ring porous; earlywood pores in rows two to three pores wide, latewood in clusters and tangential bands; vessels large in earlywood, medium in latewood, tyloses abundant; parenchyma vasicentric and aliform; rays narrow to medium, normal spacing.
Janka hardness: 1,700 lbf
Specific gravity (12% MC): 0.69
Other clue: No characteristic odor; heartwood fluoresces under blacklight, a helpful identification clue.

What Black Locust looks like

Color ranges from pale greenish-yellow to darker brown, darkening to a russet brown with age. Grain usually straight, with a medium texture. End grain: Ring porous; earlywood pores in rows two to three pores wide, latewood in clusters and tangential bands; vessels large in earlywood, medium in latewood, tyloses abundant; parenchyma vasicentric and aliform; rays narrow to medium, normal spacing.

Hardness and weight

Janka hardness 1,700 lbf (side hardness: the force needed to embed a 0.444-inch steel ball to half its diameter). Specific gravity 0.69 at 12% moisture content, so a cubic foot weighs roughly 43 lb. Weight in the hand is one of the quickest checks: compare a piece of known size against a board you already know.

Black Locust vs Osage Orange

Black locust tends toward a green or yellow tinge versus osage orange's brighter golden-yellow that ages to medium brown; unlike osage orange, black locust shavings do not release a yellow water-soluble dye when soaked in water, and black locust's heartwood fluoresces under blacklight. The Osage Orange page has its own details.

Smell, weight and other clues

No characteristic odor; heartwood fluoresces under blacklight, a helpful identification clue.

Where you will meet it

Fence posts, boatbuilding, flooring, furniture, mine timbers, railroad ties, turned objects, and veneer.

Working it

Mixed machining challenges due to density and hardness, though it responds excellently to lathe work and steam bending; has a moderate blunting effect on cutting edges; reported to cause eye and skin irritation and, less commonly, nausea.

How to photograph it for identification

Photograph a freshly cut or sanded face in daylight, not a finished or stained surface, since stain hides color and finish flattens grain. Add a close-up of the end grain: cut a clean end, wet it or sand it to 220, and shoot from straight on; pore pattern and rays are the most reliable marks. Put a ruler in frame. The app suggests the likely species; confirm with the end grain and weight.

FAQ

How hard is Black Locust?

Janka hardness 1,700 lbf. For comparison, Red Oak is about 1,290 lbf and Eastern White Pine about 380 lbf.

How do I tell Black Locust from Osage Orange?

Is Black Locust a hardwood or a softwood?

Black Locust is a hardwood: it comes from a broadleaf tree. Hardwood and softwood describe the kind of tree, not how hard the wood is; some hardwoods are softer than some softwoods.

What color is Black Locust?

Color ranges from pale greenish-yellow to darker brown, darkening to a russet brown with age.

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