Identifying Igneous Rocks

What are rocks?

Common minerals.

Sedimentary and metamorphic rocks.

Igneous Rocks

The relative amounts of just three main minerals; quartz, plagioclase feldspar, and potassium feldspar are all you need to know to start identifying igneous rocks. In addition to these three light-colored, felsic minerals, the abundance of dark, mafic minerals can also help you distinguish one type of igneous rock from another.

Once you know you have an igneous rock, look at the texture to decide if it is intrusive (big crystals) or extrusive (fine texture). Then use this chart to make your first guess based on how dark (mafic) or light (felsic) your rock appears.

To be sure you've named your rock correctly you need to compare the amounts of plagioclase feldspar, potassium feldspar, and quartz and plot it on the triangular graph.

Try this: suppose your rock is coarse-grained, so you know it's intrusive. It has 40% quartz, 30% potassium feldspar, and 30% plagioclase feldspar, it's called granite.

--Taken from USGS Geology in the Parks.

Herbarium Curation

Sagehen uses volunteers to manage its collections, including our herbarium. Here are some useful documents to help you understand the principles and strategy.

IMPORTANT! Be scrupulous about your field and lab notes. Keep a lab journal and field notebook. Document everything you do! Your effort is wasted--or even destructive--if you (and others) cannot later figure out what you did.

Organization and Management

• Sagehen Herbarium Curation and Workflow, 2020
• Sagehen Herbarium Guidelines 
• Digital collection. Sagehen's herbarium vouchers have been digitized and are available online at CCH2.org. 
• Herbarium Collection Needs & Notes, 2020

https://www.capturingcaliforniasflowers.org/workflow--protocols.html

* * * 

Thanks to all our Sagehen Herbarium volunteers to date!

• Erica Krimmel: program development; collections organization; digitizing; herbarium expansion; volunteer management.
• Alex Gallandt: accessioning; mounting; collecting; updating taxonomy; reorganizing collection schema.
• Angele Carroll: plant mounting; voucher filing
• Hannah Johansson: accessioning assistance
• All the California Naturalists and Weed Warriors who have helped at plant mounting days! 

 

Botany tools

Here are some useful tools to help you with your iNaturalist botanical observations in the Sierra Nevada.

Tools:

• See this link for information about how to choose a hand lens, and how to take better plant pictures.
• Plant collecting and documenting field notebook: with fields already printed, so you don't have to remember them all!
• This is a fantastic visual guide to cryptic and poetic botanical vocabulary.

Cheat sheets:

See this link for more information:
http://www.northernontarioflora.ca/inflorescence_types.cfm 

Field workshops:

Field courses from the California Native Plant Society, or the Jepson Herbarium will really jumpstart your identification skills. You'll also meet other botanists and enthusiasts that you can spend time with in the field. That's the trick to really learning botany.

There are workshops at all levels, and many are incredibly technical. If you are a beginner, look for "Introduction to..." courses.

Plant keys:

A dichotomous key helps you identify plants by leading you through a branching series of "This or that?" questions until you--hopefully--reach a species or finer ID. Be advised that keying can be a bit of an art and it helps to do it with a friend or three. It also helps tons to get to Family or even Genus before consulting the key, and you will definitely need a botanical dictionary to tease out the difference between arcane terms like, say, "puberulent" and "pubescent".

The Jepson Manual (TMJ2) is the 800-lb gorilla, with complete listings for California plants and an active and dynamic community constantly working to update it. Other states tear their eyes out with envy.

Unfortunately, the book itself actually weighs about 800-lbs. It's a pain in the lumbar to tote it around the field.

Fortunately, an e-Flora with the same data is on-line (for the office), and there's an e-Book version now for your iPad or other device for use in the field (by some accounts the Kindle version is more user-friendly).

Another option is the Weeden key. Less complete and up-to-date than TJM2, but very portable, it is still incredibly popular despite being out of print for a couple of decades. Keep a weather-eye out when trolling used book sales, and grab as many as you can if they're cheap--you won't have any trouble finding homes for them.

Plant keys can be tricky, and it seems to work best to use them as a group effort to smooth out the interpretation factor. You'll definitely need a good loupe to see the characters described...and sometimes a dissecting scope for some families (like, the Sunflower Family). You can use a key to get better at identifying Families by sight, which you will find really boosts your game and makes botanizing more fun!

Online Courses:

• Charles Sturt University Virtual Herbarium. Learning botany starts with understanding flowers. Once you grasp floral formulas, you can identify Families, and then you are off and running! This site has an incredible interactive tutorial and testing tools for leaves, gynoecium and floral formulae that teach you to see and understand the unique structural patterns of leaves, sepals, petals, androecium and gynoecium that make up plants and flowers, and which arrange them taxonomically.
• Lab for UC Davis Plant Sciences 102.
• "Connecting Students to Citizen Science and Curated Collections" is a fantastic introduction to plant collecting, pressing, identifying, and documenting using iNaturalist.
• Webinar on the above collections program. If you are interested in the didactics of this program, and why it includes the content it does, watch this.