Have you ever held a rock in your hand and wondered, “What kind of mineral is this?” Identifying minerals can be tricky, but one of the most effective tools for doing it is a streak plate, usually made from unglazed porcelain.

This simple piece of equipment can help you discover the true color of a mineral’s powder, which is often a key clue in figuring out what it is. You might think it’s complicated and that’s where this step-by-step guide comes in. Keep reading!

Steps In Using A Streak Plate For Mineral Identification

Identifying a mineral using a streak plate is a fundamental technique in geology and mineralogy that can provide valuable insights into the identity of a mineral. Here are several steps and tips to effectively use it for mineral identification:

Understand The Concept

Imagine you have a mineral in your hand; it looks one way on the surface, but how it looks on the inside can be different. That’s where an unglazed porcelain plate comes in. When you rub the mineral across this plate, it leaves behind a powder.

This powder reveals the mineral’s streak color, a crucial clue to identifying it. The streak test shows us the mineral’s pure color, free from any surface impurities or weathering.

This pure color, or streak, tends to be much more consistent and reliable for identification purposes than the mineral’s external color.

Consider The Hardness

Every mineral has a hardness level based on the Mohs Scale of Hardness that goes from 1 to 10. The streak test works best on minerals that are not super hard, specifically those with a hardness of less than 7 on this scale.

Softer minerals can easily leave a colorful powder on the streak plate, showing us their true colors.

If a mineral is harder than 7, however, rubbing it on a porcelain plate might not leave any streak, or it could even scratch the plate.

Choose The Right Streak Plate

Picking the right streak plate is like choosing the perfect background for a picture. You want to make sure the colors pop and are easy to see. Most of the time, a white porcelain plate is your go-to buddy.

But, here’s a cool tip: if you’re working with a mineral that’s very light-colored, almost like it’s trying to blend in with the white plate, switch things up.

Go for a black streak plate instead. The dark background offers a great contrast, making it way easier to see the streak. This little switch can make a big difference in spotting those streak colors.

Prepare The Mineral

Getting your mineral ready for the streak test is like preparing a pencil before you draw.

If you’ve got a big piece of mineral, look for a sharp edge or a pointy corner. This part is like the pencil’s tip, perfect for rubbing on the streak plate to see the color of its powder. But be careful not to press too hard and break your mineral or the plate.

If your mineral is more on the tiny side, you need a good grip but you shouldn’t crush it. Make sure you can hold onto it firmly without it poking you or slipping away.

Perform The Streak Test

When you’re ready to do the streak test, rub your mineral across it not too hard but not too soft either. It should be just enough to leave a mark. Imagine you’re trying to draw a line with it.

If you push too hard, you might break your mineral or even the plate, so be cautious in this step.

Also, remember that if your mineral is harder than the plate itself, it won’t make a streak. So, if you don’t see a streak, you have a super tough mineral on your hands.

Observe the Streak Color

After you’ve rubbed your mineral on the streak plate, the next step is to look at the color of the line it made.

Some minerals are like chameleons that always leave a white streak, no matter what color they are on the outside.

Then, there are minerals that are more straightforward, where the streak color matches what you see on the outside. And then, just to keep things interesting, some minerals throw a curveball and their streak is a totally different color!

Clean The Plate Between Tests

After you rub a mineral on the plate to see its streak color, you’ve got to clean the plate before you test another one. This is super important because you don’t want bits of the first mineral mixing with the next one.

To clean your streak plate, you can use water, a brush, or a cloth. Just give it a good scrub to get all the mineral powder off.

This way, each mineral gets to show its true colors without any confusion or mix-ups.

Use A Reference Guide

To correctly identify your mineral based on its streak, you need a little help. That’s where a mineral identification guide or database comes into play.

Look at the streak color you found and try to match it with pictures or descriptions in the guide.

But here’s the thing: minerals are complex. They have different traits that make them unique. So, besides the streak color, you also need to match their other features like hardness, luster, and specific gravity.

Repeat If Necessary

Let’s say you’ve just done a streak test on your mineral, but what if you’re not totally sure about the streak color you got the first time?

Don’t worry, it’s totally okay to double-check your work. Just grab your mineral and find a clean spot on the streak plate. Then, do the streak test again.

Rubbing the mineral on a new spot allows you to see if you get the same color streak as before. This is a smart move as it helps you be sure about what you’re seeing.

Document Your Findings

After you figure out the streak color for a mineral, write it down. Keep a special notebook or even a digital document just for your mineral adventures.

You can note down the name of the mineral (if you know it), the streak color you observed, and maybe even other cool details like how shiny it is or how hard it feels.

Over time, as you add more and more minerals to your notes, you’ll start to notice patterns. Maybe you’ll see that certain minerals always have the same streak color.