lang-en_us.json

{
  "item.tutorialmod.amethyst": "Amethyst"
}

model-item-amethyst.json

{
  "parent": "item/generated",
  "textures": {
    "layer0": "tutorialmod:item/amethyst"
  }
}

ModItems.java

public class ModItems {

    public static final DeferredRegister<Item> ITEMS =
            DeferredRegister.create(ForgeRegistries.ITEMS, TutorialMod.MOD_ID);


    public static final RegistryObject<Item> AMETHYST = ITEMS.register("amethyst",
            () -> new Item(new Item.Properties().group(ItemGroup.MATERIALS)));


    public static void register(IEventBus eventBus) {
        ITEMS.register(eventBus);
    }
}

TutorialMod.java

        IEventBus eventBus = FMLJavaModLoadingContext.get().getModEventBus();

        ModItems.register(eventBus);

        eventBus.addListener(this::setup);
        // Register the enqueueIMC method for modloading
        eventBus.addListener(this::enqueueIMC);
        // Register the processIMC method for modloading
        eventBus.addListener(this::processIMC);
        // Register the doClientStuff method for modloading
        eventBus.addListener(this::doClientStuff);

        // Register ourselves for server and other game events we are interested in
        MinecraftForge.EVENT_BUS.register(this);