Hello! I'm quite new to this, and due to my location in Central America, my access to print resources is currently (very) limited, I'm working to remedy that soon.

Where I live and work, there are often piles of sand from the nearby rivers used as aggregate in concrete construction. I often look through them for interesting specimens, and frequently come up with some similar stones - though occasional outliers as well. I'm just posting a few here of what I have found to be "interesting but common." After some online research, I'm circling some possibilities, and some rough guesses included a bit in the descriptions, but would love to hear from you. If you have any additional questions, please don't hesitate. Much thanks in advance for your thoughts and patience. Kind regards.

All of the following that I am posting here in this first post will not scratch with a metal file, except 9.

#1. Mostly translucent with banding of reds, yellows, and oranges, some quite vivid.
#2. Yellow/orange quartz? All translucent.
#3. Opaque red.
#4. Varying levels of grey translucence
#5. Reds and oranges - very translucent.

Well yes, you've been busy and have a good eye to spy those that are a little different. Thanks for the good pictures.
It looks like what you are finding are little pieces of all types of agate and jasper. Excluding #'s 9 & 10, I would guess agate, jasper, sandstone, or quartzite on all the others. The pieces you're finding are alluvial, brought by rivers to the sand you are finding them in. Agate and jasper 'layers' or seams are very common in Central America but they are usually very broken up from past geological events. The goal would be to try and find the source. To find bigger pieces of the agate and jasper you want to find the seams still insitu.
Agate and jasper are a cryptocrystalline form of quartz called 'Chalcedony'.
Here's some really good reading for you; 
http://www.quartzpage.de/agate.html

Happy Huntin' and Stay Safe Down There,
Joe