Here's what Tarte has to say:
This natural skin brightener is infused with Amazonian clay, vitamins and tea extract to moisturize and replenish skin as it adds a hint of glimmer. No matter your skin concern Amazonian clay completely neutralizes so you are left with a radiant complexion. Oily skin? Amazonian clay minimizes oil in and around pores to balance skin and keep product in place. Dry skin? This nourishing clay hydrates skin naturally to restore moisture. Combination skin? Amazonian clay will intuitively identify your skin concerns and deliver benefits to restore harmony. The result is makeup that wears better, longer and truer!
This is listed on the Tarte website (and most other cosmetics sites) as a highlighter, but just reading the description it sounds a lot more like a primer. So I'm really unclear on how exactly you're supposed to use this product and Tarte isn't being a whole lot of help here.
Sephora says to either apply it by itself or mix it with foundation, but if you read reviews it sounds like people have had success using it as a straight up primer. It does have a fair bit of pigmentation to it, so I'm not sure how well it would work in either of those applications unless it was already a fairly close match to your skintone.
As you can see from the swatch, it does have some color, but there isn't really anything illuminating about it as far as I can tell. I'm really at a loss for how what to say about this product.
I tried using it as a primer and it does seem to work fairly well in that regard. It kept my foundation in place and kept my T-zone from getting too oily. But as I mentioned, it does have a fair amount of pigmentation and it doesn't provide the slip that I usually like from my primers.
I also tried mixing the product with foundation and while I was afraid it was going to make the foundation too dark, it really didn't do anything at all. It certainly didn't provide any luminous effect.
I have really pale skin, perhaps for someone with a deeper skintone would see more effects. For me it isn't really doing much at all.
A full size is 50mL (I had a deluxe sample) and retails for $32 wherever Tarte is sold.