Boulder of orbicular rapakivi in Taivassalo, southwestern Finland

Abstract

A boulder of an orbicular rapakivi was found in Taivassalo, close to the southern contact of the Vehmaa rapakivi area in southwestern Finland. Many features, e.g. the fluorite content, the lack of signs of orogenic stress, the miarolitic cavieties and the finding-place all point to a rapakivi. The spheroids are nearly spherical, indicating that after they had finished growing in the magma, they sank and were piled upon the bottom of the magma chamber. When the interstitial magma between the spheroids crystallized, the volatiles were confined and concentrated, causing pegmatitic growth or miarolitic cavities.

Keywords

• Orbicular granite
• rapakivi
• magma