Porphyroblast: I’ve always thought that was such a neat word, maybe even interesting enough for a story. Say it out loud three times (“pore-fur-o-blast, pore-fur-o-blast, pore-fur-o-blast”). Now don’t you want to learn more, perhaps even own a few?
Porphyroblasts are those large recrystallized minerals that grow in the groundmass of a metamorphic rock, most typically in schists and gneisses. In New York State, we immediately think of the bright red almandine-pyrope garnets in the gneissic rocks in the Gore Mountain area, but the truth is the metamorphic schists and gneisses throughout New York and New England often contain garnet porphyroblasts. Unfortunately a lot of New York’s garnets are hosted in high-grade metamorphic gneiss and they don’t display crystal faces when the rocks are broken. Nevertheless they are large, colorful and fun to collect.
Last month I wrote about the Arkansas portion of Wayne County Gem and Mineral Club’s November field trip south (quartz, quartz and more quartz). But we did not stop there. After three days of collecting SiO2 in and around Mt. Ida, Arkansas, ten of us pointed our large black van east and headed to Tennessee and North Carolina. There was still a bit of space to fill in the van and in the trailer and we simply could not head north without filling all possible nooks and crannies. Here is how we did it! Continue reading
Garnet mining in New York State dates back to the late 19th century when the Barton Mine first opened in 1879. Henry Barton experimented with garnet as a harder and more durable abrasive than simple sand and after a fisherman friend told him about the prolific garnets in the Adirondacks he staked his claims and went into production (Kelsey, 2015).
Wayne County Gem and Mineral Club has decided to make 2016 the year of the Birthstone. And isn’t garnet a great way to get started!
Garnets are hard (Moh’s hardness of 6.5-7.5), or as hard or harder than quartz. As members of the isometric crystal system garnets are symmetric with three equal and perpendicular axes. Garnets are colorful: red, yellow, green and many shades of each. And garnet is the birthstone for all born in January.