Late-magmatic granitic fluids are typically enriched in Si, K and rare lithophile elements, including Be, Li, Sn, W, Rb, Cs, Nb, Ta, REE and U, and are also characterised by volatile components such as OH, F and B. Consequently the resultant pegmatite bodies are very coarse-grained and contain accessory minerals with unusual mineral chemistries. Pegmatites, usually present as veins, can occur as emanations from granite bodies or be produced by granite fronts generated by migmatisation during high-grade metamorphism. The former process is represented in the sites by Loch Avon; located within the Main Granite of the Cairngorms, this is the area where large topaz crystals, renowned for their blue colour, are found along with cairngorm and citrine varieties of quartz. Rare beryllium minerals, genthelvite and bertrandite, also occur. The latter process was responsible for the generation of the South Harris and Loch Nevis pegmatite suites which collectively encompass a range of mineral assemblages as follows. The Chaipaval Pegmatite site, some 2 km long, and previously worked for potassium feldspar, contains an unusual suite of uranium-bearing minerals together with spessartine, columbite and gahnite. By contrast the Sletteval Pegmatite site, also previously worked, is more thorium-rich and again contains the rare mineral thorogummite. The more mafic biotite-magnetite-bearing Loch a’ Sgurr Pegmatite site presents an intimate association of uraninite with magnetite, monazite and feldspar. The mica pegmatites at the Loch Nevis site, which formed a series of concordant lenses and veins, were rich in extractable muscovite. Additionally garnet and minor beryl are present in some pegmatites.

晚岩浆岩浆流体通常富集 Si、K 和稀有的亲石元素，包括 Be、Li、Sn、W、Rb、Cs、Nb、Ta、REE 和 U，还具有 OH、F 等挥发性组分的特征和 B. 因此，生成的伟晶岩体非常粗粒，并含有具有不寻常矿物化学性质的副矿物。伟晶岩通常以脉状存在，可以作为花岗岩体的放射物出现，也可以由高级变质作用期间混合作用产生的花岗岩锋产生。前一个过程由 Loch Avon 在站点中代表；位于 Cairngorms 的主要花岗岩内，这里有大型托帕石晶体，以其蓝色而闻名，以及 cairngorm 和黄水晶品种的石英。稀有的铍矿物、镁钙铁矿和贝氏矿也有出现。后一个过程负责产生南哈里斯和尼维斯湖伟晶岩组，这些伟晶岩组共同包含以下一系列矿物组合。Chaipaval 伟晶岩遗址长约 2 公里，以前曾用于生产钾长石，其中包含一组不寻常的含铀矿物，以及锰铝榴石、铌铁矿和辉长石。相比之下，之前也曾开采过的 Sletteval 伟晶岩矿点富含钍，并再次含有稀有矿物 throgummite。含有更多镁铁质黑云母-磁铁矿的 Loch a' Sgurr 伟晶岩遗址呈现出铀矿与磁铁矿、独居石和长石的密切结合。尼维斯湖遗址的云母伟晶岩形成了一系列一致的晶状体和脉络，富含可提取的白云母。