Igneous Rocks · common

Syenite

Syenite is a coarse-grained intrusive igneous rock composed mainly of alkali feldspar with minor amounts of dark minerals like hornblende or biotite, and it is distinguished from granite chiefly by containing little to no quartz. It forms from the slow cooling of silica-undersaturated to silica-saturated magmas at depth, allowing large, visible crystals to develop. Syenite's name derives from Syene, the ancient name for Aswan, Egypt, though the rock originally described there under that name is now known to actually be granite.

Photo: James St. John · Wikimedia Commons · CC BY 2.0

Syenite properties at a glance

Type	Igneous Rocks
Mohs hardness	5.5–6.5
Luster	Vitreous (feldspar crystals)
Fracture	Uneven
Specific gravity	2.6–2.8
Transparency	Opaque
Common colors	Gray, Pink, White, Light green
Rarity	common

Geology & background

Syenite crystallizes slowly at depth from magmas that are relatively enriched in alkali elements like sodium and potassium but poor enough in silica that quartz does not form in significant amounts, often in association with continental rift zones or alkaline igneous provinces. Notable localities include the Larvik region of Norway, source of the distinctive blue-sheen larvikite variety used widely as an ornamental building stone, the Bancroft area of Ontario, and various alkaline complexes in South Africa and Russia's Kola Peninsula. Some syenites grade into nepheline syenite, a related rock type containing the feldspathoid mineral nepheline in place of quartz, reflecting an even more silica-poor parent magma.

Rockhounds visiting classic syenite terrain should look for large, well-formed alkali feldspar crystals and, in alkaline complexes, accessory minerals such as sodalite, aegirine, or rare-earth phosphates that make these rocks a favorite among collectors interested in unusual igneous chemistry. Polished slabs of larvikite are common in building supply showrooms, making it one of the few syenites an average collector can examine up close without visiting a quarry.

How to identify Syenite

Syenite is typically light to medium gray, pink, or greenish, coarse-grained enough to show interlocking feldspar crystals with the naked eye, and it has an overall hardness around 6 reflecting its feldspar content. It lacks distinct rock-scale cleavage but its individual feldspar crystals show characteristic cleavage planes, and it can display a granular to slightly porphyritic texture depending on cooling history. Syenite closely resembles granite but is distinguished by its scarcity or absence of visible quartz grains, which appear glassy and clear in granite but are largely or entirely missing from syenite's mineral assemblage.

Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
Use multiple photos when possible, including a fresh surface and a close view of texture.

Where Syenite is found

Reported from multiple localities worldwide; verify locality against specimen provenance when available.

How much is Syenite worth?

Entry-level specimen	$1
Typical collector specimen	$10
Premium specimen	$75+

Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.

Common uses

Field identification
Construction or aggregate when suitable
Landscape interpretation
Education

Interesting facts

Syenite takes its name from ancient Syene, now Aswan, Egypt, even though the rock originally quarried there for obelisks and monuments has since been reclassified as granite rather than true syenite.
Larvikite, a striking blue-gray variety of syenite from Norway, displays an iridescent schiller effect on polished surfaces and is a popular building stone marketed as "blue pearl granite" despite not being granite at all.
Nepheline syenite, a silica-poor cousin of ordinary syenite, is mined as an industrial source of alumina and alkalis for glass and ceramics manufacturing.